[mdatagen] Define featuregates in metadata.yaml

[dmitryax]

We can define feature gates in the metadata.yaml and generate code + documentation from it. We can use the following YAML structure with a docker stats feature gate as an example:

feature_gates:
  - id: receiver.dockerstats.useScraperV2
    description: |
      When enabled, the receiver will use the function ScrapeV2 to collect metrics. 
      This allows each metric to be turned off/on via config. 
      The new metrics are slightly different to the legacy implementation.
    from_version: 0.60.0
    to_version: 0.74.0
    stage: stable
    reference_url: https://github.com/open-telemetry/opentelemetry-collector-contrib/issues/9794

[mx-psi]

Duplicate of #11634? We can keep both open I guess, since mine is more specific about each component that would need changes

[dmitryax]

Duplicate of #11634? We can keep both open I guess, since mine is more specific about each component that would need changes

Right. I wasn't aware of that issue, sorry. We can use that one for making use of this feature and this one for introducing the capability itself.

[lavishpal]

@dmitryax Could you assign this issue to me and it will be helpful if you provide guidance on how to get started?

[narcis96]

As discussed with @mx-psi, I am taking care of it