docs: add migration guide from backstage chart (1.y) to rhdh chart (2.y) [RHIDP-16514] - #516

No file matched to [/home/runner/work/rhdh-chart/rhdh-chart/**/*requirements*.txt,/home/runner/work/rhdh-chart/rhdh-chart/**/*requirements*.in,/home/runner/work/rhdh-chart/rhdh-chart/**/*constraints*.txt,/home/runner/work/rhdh-chart/rhdh-chart/**/*constraints*.in,/home/runner/work/rhdh-chart/rhdh-chart/**/pyproject.toml,/home/runner/work/rhdh-chart/rhdh-chart/**/uv.lock,/home/runner/work/rhdh-chart/rhdh-chart/**/*.py.lock]. The cache will never get invalidated. Make sure you have checked out the target repository and configured the cache-dependency-glob input correctly.