CDAT 8.2.1 Release

[jasonb5]

Use this issue to track 8.2.1 release progress.

• Build CDAT RC 8.2.1.rc1
• update readthedocs env file for cdms and vcs
• Build CDAT RC 8.2.1.rc2
• Pass testing
• Build CDAT Release
• Update documentation

List might change.

[jasonb5]

Just noting these non-blocking issues.

• Test fails for dv3d dv3d#30
• Test fails for VCSAddons vcsaddons#54

[muryanto1]

Test logs are:
https://app.circleci.com/pipelines/github/CDAT/cdat_validate_release/19/workflows/aec34ba1-3cee-46a4-bd6a-44c370afe883