Release v0.21.0

[asjohnston-asf]

Golden test ran to completion, but the comparison results don't contribute anything to validating these changes. A baseline run (prior to merging any changes) failed with a variety of "Data arrays are different shapes" and " Reference and secondary Dataset objects are not close" warnings.

Run prior to merging this change to develop: https://github.com/ASFHyP3/hyp3-testing/actions/runs/11334018017/job/31519336013

Run after merging this change to develop: https://github.com/ASFHyP3/hyp3-testing/actions/runs/11336345131/job/31526111047

[github-actions]

Developer checklist

• Indicated the level of changes to this package by affixing one of these labels:
  • major -- Major changes to the API that may break current workflows
  • minor -- Minor changes to the API that do not break current workflows
  • patch -- Patches and bugfixes for the current version that do not break current workflows
  • bumpless -- Changes to documentation, CI/CD pipelines, etc. that don't affect the software's version
• (If applicable) Updated the dependencies and indicated any downstream changes that are required
• Added/updated documentation for these changes
• Added/updated tests for these changes
• Verified changes in test deployment and summarized results, e.g. in PR description or comments on the related issue(s)

Reviewer checklist

• Have all dependencies been updated?
• Is the level of changes labeled appropriately?
• Are all the changes described appropriately in CHANGELOG.md?
• Has the documentation been adequately updated?
• Are the tests adequate?
• Have the changes been verified in the test deployment?