Cody: Implemented generate release notes recipes

[deepak2431]

This PR is for issue sourcegraph/cody#187.

Test plan

All unit tests and integration tests have passed.
Testing on multiple repos with no tags, tags.
Some of the sample generated output of release notes:

[deepak2431]

@abeatrix Can you review this please, Thanks in advance!

[abeatrix]

@deepak2431 this is so cool!

Will review first thing next week!

[deepak2431]

Sure, Take your time!

[abeatrix]

Works for Cody too which is cool! Could you add the new change to the CHANGELOG for cody please? @deepak2431

[deepak2431]

Thanks for the review @abeatrix. Glad it worked well for Cody too. I have added the changelog.
One thing I would like to mention is that when you enable auto-merge, the PR doesn't get merged; not sure why. So, I think after approval, you need to merge it manually. As PR #51519 is still unmerged.

[abeatrix]

Thanks! There is a conflict with the CHANGELOG. Once the conflict has been resolved I can try to run the pipeline again.

For future references, you can also tag the sourcegraph/cody team as reviewer so anyone on the team can help you with the review and you won't get blocked by me :)

[deepak2431]

Thanks! There is a conflict with the CHANGELOG. Once the conflict has been resolved I can try to run the pipeline again.

For future references, you can also tag the sourcegraph/cody team as reviewer so anyone on the team can help you with the review and you won't get blocked by me :)

I have updated the PR by resolving the conflicts. That will be great, I will keep in mind from the next time to tag sourcegraph/cody team in PR.

[philipp-spiess]

Looking into getting this into todays release, thank you so much for it :)