docs(spanmetrics): Fix feature gate name in README (open-telemetry#43626)

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Hello! It looks like
open-telemetry#41865
introduced a new feature flag and associated docs. The docs list it as
`connector.spanmetrics.includeServiceInstanceID`, but I believe it's
actually `connector.spanmetrics.includeCollectorInstanceID`. Looks like
it might've changed due to feedback in the PR

Passing `connector.spanmetrics.includeServiceInstanceID` resulted in the
following error for me:

> "Error: invalid argument
"connector.spanmetrics.includeServiceInstanceID" for "--feature-gates"
flag: no such feature gate
"connector.spanmetrics.includeServiceInstanceID". valid gates:
[awsemf.nodimrollupdefault clickhouse.json
cloudfoundry.resourceAttributes.allow confighttp.framedSnappy
confmap.enableMergeAppendOption connector.datadogconnector.NativeIngest
connector.servicegraph.legacyLatencyMetricNames
connector.servicegraph.legacyLatencyUnitMs
connector.servicegraph.virtualNode
connector.spanmetrics.excludeResourceMetrics
connector.spanmetrics.includeCollectorInstanceID
connector.spanmetrics.legacyMetricNames
connector.spanmetrics.useSecondAsDefaultMetricsUnit
datadog.EnableOperationAndResourceNameV2
datadog.EnableReceiveResourceSpansV2 exporter.PersistRequestContext
exporter.awsxray.skiptimestampvalidation
exporter.datadogexporter.DisableAPMStats
exporter.datadogexporter.InferIntervalForDeltaMetrics
exporter.datadogexporter.TraceExportUseCustomHTTPClient
exporter.datadogexporter.UseLogsAgentExporter
exporter.datadogexporter.metricexportnativeclient
exporter.datadogexporter.metricexportserializerclient
exporter.datadogexporter.metricremappingdisabled
exporter.googlecloud.CustomMonitoredResources
exporter.googlemanagedprometheus.intToDouble
exporter.kafkaexporter.UseFranzGo
exporter.prometheusexporter.DisableAddMetricSuffixes
exporter.prometheusremotewritexporter.EnableMultipleWorkers
exporter.prometheusremotewritexporter.RetryOn429
exporter.prometheusremotewritexporter.enableSendingRW2
exporter.xray.allowDot
extension.jaegerremotesampling.replaceThriftWithProto
extension.sumologic.updateCollectorMetadata filelog.allowFileDeletion
filelog.allowHeaderMetadataParsing filelog.decompressFingerprint
filelog.mtimeSortType filter.filterlog.useOTTLBridge
filter.filtermetric.useOTTLBridge filter.filterspan.useOTTLBridge
hostmetrics.process.bootTimeCache
k8sattr.fieldExtractConfigRegex.disallow
k8sattr.labelsAnnotationsSingular.allow logs.assignKeys
logs.jsonParserArray metricsgeneration.MatchAttributes
otelcol.printInitialConfig parser.uri.ecscompliant
pdata.enableRefCounting pdata.useCustomProtoEncoding
pdata.useProtoPooling pkg.translator.prometheus.NormalizeName
pkg.translator.prometheus.PermissiveLabelSanitization
postgresqlreceiver.preciselagmetrics
processor.resourcedetection.propagateerrors
processor.resourcedetection.removeGCPFaasID
processor.tailsamplingprocessor.disableinvertdecisions
processor.tailsamplingprocessor.metricstatcountspanssampled
processor.tailsamplingprocessor.recordpolicy
processor.transform.ConvertBetweenSumAndGaugeMetricContext
receiver.azureeventhubreceiver.UseAzeventhubs
receiver.datadogreceiver.Enable128BitTraceID
receiver.hostmetricsreceiver.UseLinuxMemAvailable
receiver.jaeger.DisableRemoteSampling
receiver.kafkametricsreceiver.UseFranzGo
receiver.kafkareceiver.UseFranzGo receiver.mongodb.removeDatabaseAttr
receiver.postgresql.connectionPool
receiver.postgresql.separateSchemaAttr
receiver.prometheusreceiver.EnableCreatedTimestampZeroIngestion
receiver.prometheusreceiver.EnableNativeHistograms
receiver.prometheusreceiver.RemoveLegacyResourceAttributes
receiver.prometheusreceiver.RemoveStartTimeAdjustment
receiver.prometheusreceiver.UseCollectorStartTimeFallback
receiver.prometheusreceiver.UseCreatedMetric
receiver.sqlserver.RemoveServerResourceAttribute
receiver.vcenter.resourcePoolMemoryUsageAttribute
receiverhelper.newReceiverMetrics service.AllowNoPipelines
service.noopTracerProvider service.profilesSupport
stanza.synchronousLogEmitter
telemetry.UseLocalHostAsDefaultMetricsAddress
telemetry.disableHighCardinalityMetrics telemetry.newPipelineTelemetry
transform.flatten.logs]"

So here I just fix the name in the docs.

#### Description

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#### Link to tracking issue
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<!--Describe what testing was performed and which tests were added.-->
#### Testing

I copy pasted the flag name string from the doc change into my
dockerfile and made sure it ran (no typos).

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#### Documentation

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Just updating `connector/spanmetricsconnector/README.md` as described
above.

----

Thanks for the feature!

Co-authored-by: Alex Boten <[email protected]>

Author: liamfd

connector/spanmetricsconnector/README.md

@@ -62,9 +62,9 @@ across all spans:
 - `status.code`
 - `collector.instance.id`
 
-The `collector.instance.id` dimension is intended to add a unique UUID to all metrics, ensuring that the spanmetrics connector 
+The `collector.instance.id` dimension is intended to add a unique UUID to all metrics, ensuring that the spanmetrics connector
 does not violate the **Single Writer Principle** when spanmetrics is used in a multi-deployment model.
-Currently, `collector.instance.id` must be manually enabled via the feature gate: `connector.spanmetrics.includeServiceInstanceID`.
+Currently, `collector.instance.id` must be manually enabled via the feature gate: `connector.spanmetrics.includeCollectorInstanceID`.
 More detail, please see [Known Limitation: the Single Writer Principle](#known-limitation-the-single-writer-principle)
 
 ## Span to Metrics processor to Span to metrics connector
@@ -283,7 +283,7 @@ connectors:
       - telemetry.sdk.language
       - telemetry.sdk.name
 ```
-* Manually enable the feature gate: `connector.spanmetrics.includeServiceInstanceID` to produce uniquely identified metrics.
+* Manually enable the feature gate: `connector.spanmetrics.includeCollectorInstanceID` to produce uniquely identified metrics.
 * For exporters like Prometheus, which rely on the single writer assumption, use a dedicated pipeline with a single `spanmetricsconnector` instance
 
 More context is available in [GitHub issue #21101](https://github.com/open-telemetry/opentelemetry-collector-contrib/issues/21101).