[cmd/opampsupervisor] Add support for local Collector config file via agent.config_file

[tigrannajaryan]

Component(s)

cmd/opampsupervisor

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

The spec says:

The Supervisor creates a Collector config file in a temp directory and passes to the Collector via --config command line option. The config file is created by merging the local config file (optional) and the remote config received from OpAMP backend (also optional).

The spec also defines how the local config file path is specified in the supervisor config:

agent:
  # Path to optional local Collector config file to be merged with the
  # config provided by the OpAMP server.
  config_file: /etc/otelcol/config.yaml

This feature is not yet implemented in the Supervisor.

Describe the solution you'd like

See the spec: https://github.com/open-telemetry/opentelemetry-collector-contrib/tree/main/cmd/opampsupervisor/specification

Describe alternatives you've considered

No response

Additional context

No response

[github-actions]

Pinging code owners:

• cmd/opampsupervisor: @evan-bradley @atoulme @tigrannajaryan

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[crobert-1]

Removing needs triage as this makes sense to me and was filed by a code owner.