Add internal localhostgate package

[mx-psi]

Description:

Follow up to open-telemetry/opentelemetry-collector/pull/8622

Link to tracking Issue: First step of #30702

[songy23]

Should there be a changelog or a README for the feature gate?

[mx-psi]

Should there be a changelog or a README for the feature gate?

I was thinking we can do a changelog item once we actually use it in individual components, listing all the components we are using this in. I can also add the changelog item now with an empty list of components if you think that's better

[songy23]

Yes I think it makes sense to start a list now and expand it when changes are made to each component.

[crobert-1]

I'm wondering if there's a good way to enforce keeping this up to date core. There will be times they differ, but it should only be temporarily. There should be a PR opened for both repositories, one will just get merged before the other.

It could be a CI check that simply fails whenever a user changes the contents of these files, warning the user that core needs updated as well. A triager, approver, or maintainer could then come, confirm a PR is also opened against core, and then add some kind of skip label that ignores the check? Or just approve and merge it with the failing CI action knowing it's not an issue. If it's a CI action it would also need to be in core to make sure contrib stays up to date as well.

Otherwise we could add a CI action that simply compared file contents and fails when they don't match. This would be a bit more involved and would fail in unrelated PRs, which would be confusing.

I don't want to make it too complicated but speaking from experience, a comment at the top of a file is pretty easy to miss.

[mx-psi]

@crobert-1 I don't expect much to change here, but it makes sense to have something like this. I filed #30793 to do this, but I would like to do it separately (I want to unblock PRs that start to use this feature gate in components)

[songy23]

Needs make tidy