fix(CI): Add step to create PR instead of direct commit

[anurag-rajawat]

Description

This PR updates the stable release job to create a new PR in the Nimbus repo to update the helm charts version.

Does this PR introduce a breaking change?
No.

Checklist

• PR title follows the <type>: <description> convention
• I use conventional commits in my commit messages
• I have updated the documentation accordingly
• I Keep It Small and Simple: The smaller the PR is, the easier it is to review and have it merged
• I have performed a self-review of my code
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Additional information for reviewer

Mention if this PR is part of any design or a continuation of previous PRs