Adding Snapshot additional mapping tokens

[rajrku]

Closes: https://github.com/github/actions-larger-runners/issues/3170

Adding new mapping tokens to snapshot yaml keyword Added tests to validate the mapping token changes to snapshot keyword

Format:

- snapshot:
   - image-name: blah-blah
   - version: <major-version>.*
   - if: <conditions-similar-to-job-if>