stac_io as argument to Catalog.save

[fnattino]

Related Issue(s):

Closes #666

Description:
Add the possibility of providing a StacIO instance to write out a catalog, as useful e.g. to read from and write to different file systems.

PR Checklist:

• Code is formatted (run pre-commit run --all-files)
• 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-commenter]

Codecov Report

Merging #751 (64042bc) into main (8b8ad7e) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #751      +/-   ##
==========================================
+ Coverage   94.39%   94.42%   +0.02%     
==========================================
  Files          77       77              
  Lines       11298    11312      +14     
  Branches     1343     1346       +3     
==========================================
+ Hits        10665    10681      +16     
+ Misses        455      453       -2     
  Partials      178      178              

Impacted Files	Coverage Δ
pystac/catalog.py	92.15% <100.00%> (ø)
tests/test_catalog.py	99.00% <100.00%> (+0.01%)	⬆️
tests/utils/stac_io_mock.py	92.59% <0.00%> (+7.40%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 8b8ad7e...64042bc. Read the comment docs.

[duckontheweb]

Thanks for contributing this @fnattino !