Include collection assets in make_all_asset_hrefs_relative/absolute

[jsignell]

Related Issue(s):

• stac copy --copy-assets does not copy collection assets stactools#423

Description:

Broadly "all_assets" for a catalog should include collection assets. Specifically I needed this functionality to solve the stactools issue

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.

[ircwaves]

I don't think my suggestion is required, but it reads cleaner to my brain. As a bonus, a commit will bonk the CI when landsat's stac-api is back up and running.

[codecov]

Codecov Report

Patch coverage: 62.50% and project coverage change: -0.11 ⚠️

Comparison is base (d88fba8) 92.06% compared to head (429b26b) 91.96%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1168      +/-   ##
==========================================
- Coverage   92.06%   91.96%   -0.11%     
==========================================
  Files          50       50              
  Lines        6708     6720      +12     
  Branches      990      994       +4     
==========================================
+ Hits         6176     6180       +4     
- Misses        357      365       +8     
  Partials      175      175              

Impacted Files	Coverage Δ
pystac/collection.py	92.85% <44.44%> (-3.36%)	⬇️
pystac/item.py	93.98% <66.66%> (+0.73%)	⬆️
pystac/catalog.py	93.37% <100.00%> (+0.02%)	⬆️

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