Replace validate_has_extension with ensure_has_extension

[jamesfisher-geo]

Related Issue(s):

• validate_has_extension is a bad name for a method that has can modify the object #1061

Description:
Deprecated ExtensionManagementMixin.validate_has_extension and replaced with ExtensionManagementMixin.ensure_has_extension. Calling ExtensionManagementMixin.validate_has_extension will raise a DeprecationWarning and call ExtensionManagementMixin.ensure_has_extension

PR Checklist:

• pre-commit hooks pass locally
• Tests pass (run scripts/test)
• Documentation has been updated to reflect changes, if applicable
• This PR maintains or improves overall codebase code coverage.
• Changes are added to the CHANGELOG. See the docs for information about adding to the changelog.

[codecov]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Files	Coverage Δ
pystac/extensions/datacube.py	80.06% <100.00%> (ø)
pystac/extensions/eo.py	93.17% <100.00%> (ø)
pystac/extensions/grid.py	96.22% <100.00%> (ø)
pystac/extensions/item_assets.py	95.37% <100.00%> (ø)
pystac/extensions/label.py	93.31% <100.00%> (ø)
pystac/extensions/mgrs.py	98.70% <100.00%> (ø)
pystac/extensions/pointcloud.py	97.81% <100.00%> (ø)
pystac/extensions/projection.py	97.08% <100.00%> (ø)
pystac/extensions/raster.py	90.22% <100.00%> (ø)
pystac/extensions/sar.py	98.56% <100.00%> (ø)
... and 10 more

... and 6 files with indirect coverage changes

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