[charts] add GHA job for validating againts rc image dependencies

[nicholasSUSE]

Problem

Recently on the v2.10.0 release cycle, prometheus-federator was released as an UnRc'ed version, however it was pointing for dependencies that were still rc versions, see the values.yaml field tag:
rancher/charts@400a581#diff-55eb77103e4e30ec80dc204fb901bf33108d134771793e334086c81bd1f1ea57

This should never happen.

Solution

Implement a GHAction Job to check all tag fields from value.yaml files and make sure they do not contain a rc version in the field.

The job must only run on release-v2.* branches.