ci: Automate code-freeze

[ko3n1g]

What does this PR do ?

This forks the release-branch by either maintaining the pre-release tag or by dropping it. It also raises a PR against main to bump the pre-release tag or drop and bump the minor tag. Finally, it sends a Slack notification about the release-branch

Changelog

• Please update the CHANGELOG.md under next version with high level changes in this PR.

Usage

• You can potentially add a usage example below

# Add a code snippet demonstrating how to use this 

Before your PR is "Ready for review"

Pre checks:

• [ ] Make sure you read and followed Contributor guidelines
• [ ] Did you write any new necessary tests?
• [ ] Did you add or update any necessary documentation? Make sure to also update the NeMo Framework User Guide which contains the tutorials

Checklist when contributing a new algorithm

• [ ] Does the trainer resume and restore model state all states?
• [ ] Does the trainer support all parallelism techniques(PP, TP, DP)?
• [ ] Does the trainer support max_steps=-1 and validation?
• [ ] Does the trainer only call APIs defined in alignable_interface.py?
• [ ] Does the trainer have proper logging?

Additional Information

• Related to # (issue)