Release 0.8.9 - Water masking documentation

[hjkristenson]

This PR adds a page documenting the water mask used for InSAR processing. It also updates the references to the asf_tools python package to the most recent release.

[github-actions[bot]]

Developer checklist

• [x] 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
• [x] (If applicable) Updated the dependencies and indicated any downstream changes that are required
• [x] 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

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