ci: Add new workflow for releasing turtles providers chart

[yiannistri]

What this PR does / why we need it:

This PR introduces a new release workflow for the providers chart, to bring it inline with the turtles chart release process. The main issue being addressed is that it no longer requires an new commit to set the version number for the providers chart, whenever a release happens. Instead, the workflow runs as part of a release (invoked manually at release time) to create a PR that bumps the providers chart version with the correct version number.

Prerequisites for this to work:

• permissions granted to create a PR in rancher/prime-charts (currently in progress)
• the ability to point to a commit SHA of a release branch in order to identify the version of the providers chart to be released/bumped (needs input from release team)

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #2236

Special notes for your reviewer:

Checklist:

• squashed commits into logical changes
• includes documentation
• adds unit tests
• adds or updates e2e tests