Zilla is validating `env` vars before replacing them.

[vordimous]

Describe the bug
Zilla is validating env vars before replacing them.

[23,31][/telemetry/exporters/prometheus_metric_exporter/options/endpoints/0/port] The value must be of integer type, but actual type is string.
error
io.aklivity.zilla.runtime.engine.config.ConfigException: Engine configuration failed

To Reproduce

docker run -v ./zilla.yaml:/etc/zilla/zilla.yaml --env PORT="7190" ghcr.io/aklivity/zilla:0.9.68 start -v

zilla.yaml

---
name: example
bindings:
  north_tcp_server:
    type: tcp
    kind: server
    options:
      host: 0.0.0.0
      port: 12345
    exit: north_echo_server
  north_echo_server:
    type: echo
    kind: server

telemetry:
  exporters:
    prometheus_metric_exporter:
      type: prometheus
      options:
        endpoints:
          - scheme: http
            path: /metrics
            port: ${{env.PORT}}

[vordimous]

Looks like this just fixed one issue. Running the redpanda-doom-demo has a vailed validation on the sasl.mechanism though the env variable is a valid value.

Exactly one of the following sets of problems must be resolved.
1) [116,51][/bindings/south_redpanda_client/options/sasl/mechanism] The value must be constant string "plain".
2) [116,51][/bindings/south_redpanda_client/options/sasl/mechanism] The value must be constant string "scram-sha-1".
3) [116,51][/bindings/south_redpanda_client/options/sasl/mechanism] The value must be constant string "scram-sha-256".
4) [116,51][/bindings/south_redpanda_client/options/sasl/mechanism] The value must be constant string "scram-sha-512".
error
io.aklivity.zilla.runtime.engine.config.ConfigException: Engine configuration failed

Perhaps any zilla.yaml property that has a restricted value could have this issue when it is set via an env var?