[release] Autopopulate release notes in Github release

[mx-psi]

Currently, the release manager needs to manually copy release notes from CHANGELOG.md and CHANGELOG-API.md into the Github release. This is easy to forget, and a step that could be automated. We should automate it!

Part of the retro for v0.100.0 release.

[animeshdas2000]

Hi @mx-psi, if I understand it right, we are looking to automate the release notes from the Github releases section? I am happy to contribute

[mx-psi]

Hi @mx-psi, if I understand it right, we are looking to automate the release notes from the Github releases section? I am happy to contribute

Yes! So e.g. we would add the release notes here https://github.com/open-telemetry/opentelemetry-collector/releases/tag/v0.101.0 (which were added manually) in an automated way. Assigned to you :)

[animeshdas2000]

Great thanks. Let me get started, I'll share an update soon :)

[animeshdas2000]

I have gone through the release process in RELEASE.md. I saw the workflow file builder-release.yaml runs when there's a new release to be done. Just want to confirm if this is the last step in the release process where we create this release.

Snippet from builder-release.yaml

- name: Create Github Release 
    run: | 
          gh release create ${{ github.ref_name }} -t ${{ github.ref_name }} -n 
         "### Images and binaries here: https://github.com/open-telemetry/opentelemetry-collector-releases/releases/tag/${{ github.ref_name }}"

If so, assuming the CHANGELOG.md and CHANGELOG-API.md would've been populated with the latest release notes. I'll just fetch it from the respective files as add it here itself.

Alternatively, if I've understood this incorrectly. Please let me know

[mx-psi]

@animeshdas2000 I think that's right, yes. Those files should have been populated in a previous step of the release, so you can fetch its contents if that's the easiest way to go about this.

[animeshdas2000]

@mx-psi I have written a script which extracts all the relevant changelog. I need to test it with github actions, what's the best apporach you'd suggest. Since this is a part of release I am not sure how this should be tested. Although I've tested it locally.

[mx-psi]

@animeshdas2000 You should be able to test it by forking this repository and making a test release on that repository (you can do the fork by clicking on the 'Fork' button at the top of https://github.com/open-telemetry/opentelemetry-collector).