[exporter/elasticsearch] Set user-agent header

[strawgate]

Component(s)

exporter/elasticsearch

Is your feature request related to a problem? Please describe.

The Elasticsearch exporter doesn't set the User-Agent header in the outgoing HTTP requests it makes, but it should.

Describe the solution you'd like

Following the pattern set in the otlphttpexporter, it should use fmt.Sprintf("%s/%s (%s/%s)", set.BuildInfo.Description, set.BuildInfo.Version, runtime.GOOS, runtime.GOARCH) as the user agent value.

Describe alternatives you've considered

No response

Additional context

No response

[github-actions]

Pinging code owners:

• exporter/elasticsearch: @JaredTan95

See Adding Labels via Comments if you do not have permissions to add labels yourself.