Allow future extensions to be used

[jsignell]

Related Issue(s):

• Closes Rework extensions to handle "future" versions correctly #1226

Description:

When loading extension data, extension implementations should use startswith (or whatever) to detect the presence of the extension, not an exact string match.

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: 6 lines in your changes are missing coverage. Please review.

Files	Coverage Δ
pystac/extensions/classification.py	96.03% <100.00%> (-0.37%)	⬇️
pystac/extensions/mgrs.py	98.70% <100.00%> (+0.01%)	⬆️
pystac/extensions/base.py	92.30% <80.00%> (-2.22%)	⬇️
pystac/extensions/eo.py	93.17% <50.00%> (-0.76%)	⬇️
pystac/extensions/grid.py	96.22% <50.00%> (-3.78%)	⬇️
pystac/extensions/label.py	93.31% <50.00%> (-0.53%)	⬇️
pystac/extensions/projection.py	97.08% <50.00%> (-1.44%)	⬇️
pystac/extensions/raster.py	90.22% <66.66%> (-0.57%)	⬇️

📢 Thoughts on this report? Let us know!.

[gadomski]

One nit that you should feel free to ignore but LGTM other than needs CHANGELOG.