Update metadata json in preparation for 6.1 release

[TravisEz13]

PR Summary

update metadata json in preparation for 6.1 release

• ReleaseTag is now StableReleaseTag
• NextReleaseTag is not PreviewReleaseTag
• Added ServicingReleaseTag for the N-1 Stable release

The old names will be removed after we release.
FYI, @DarwinJS in case you use this.

PR Checklist

• PR has a meaningful title
  • Use the present tense and imperative mood when describing your changes
• Summarized changes
• Change is not breaking
• Make sure all .h, .cpp, .cs, .ps1 and .psm1 files have the correct copyright header
• This PR is ready to merge and is not Work in Progress.
  • If the PR is work in progress, please add the prefix WIP: to the beginning of the title and remove the prefix when the PR is ready.
• User-facing changes
  • Not Applicable
  • OR
  • User-facing Documentation needed
    • Issue filed - Issue link:
• Testing - New and feature
  • Not Applicable or can only be tested interactively
  • OR
  • Make sure you've added a new test if existing tests do not effectively test the code changed
    • Add [feature] if the change is significant or affects feature tests

[daxian-dbw]

LGTM

[DarwinJS]

Was this already discussed somewhere? Not exactly a lot of time given to assess and remediate dependencies.