[CNSL-1935] Add automated release PR workflow

[linhcrl]

Added GitHub Actions workflow that automatically creates release PRs when automation/pending-deploy-* branches are merged to main. The workflow updates go.mod and main.go for major version changes, updates config.yaml with the new version, and regenerates the OpenAPI client to automatically update all generated files (README.md, docs/README.md, pkg/client/configuration.go, and other generated code).

Example PR: https://github.com/cockroachlabs/cockroach-cloud-sdk-go-automation-testing/pull/185

[linhcrl]

Tested this locally and it worked as expected

[github-actions]

No breaking changes detected.

[fantapop]

thanks for including the sample images. I noticed that the Changelog entries are extremely long. I think we'll want to experiment with the prompt we're using to build those.

[linhcrl]

@fantapop I've updated the reusable action to remove changelog entries from the commit message body.

Why: Commit message lines should be at most 72 characters, but changelog entries don't follow this rule. It would be unnecessarily complex to convert the changelog entries to wrap at 72 characters for the commit message. Since the individual commits already describe the changes and the changelog entries are visible in the PR description, the simpler approach is to use a hardcoded message format.

Here's the PR: cockroachdb/actions#27

[fantapop]

yeah makes sense. I didn't think it was coming from this PR. It just looked long and agent generated. You hand crafted it though?

I did use claude to write it. It's the changelog entry for this PR. I'was just trying to say it's not autogenerated by a workflow based on any prompt. I can update the relevant PR to make the entry shorter but it's a one off

ah I see. makes sense. we are planning to generate the changelog entry from claude though right? We should consider asking it to keep it brief.

[fantapop]

This is looking good to me. It seems like we could get away with logging to stdout for info lines and stderr for warn and error lines.