Raise an error on APILayoutStrategy when root_href is non-url

[jsignell]

Related Issue(s):

• closes Disallow saving to the filesystem when using APILayoutStrategy #1486

Description:

Doesn't strictly disallow saving. Saving to a URL already throws an error if you are using the default stac_io so I think it is more appropriate to raise an error if you try to set the root to a non-url

PR Checklist:

• Pre-commit hooks and 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

All modified and coverable lines are covered by tests ✅

Project coverage is 91.46%. Comparing base (67931b5) to head (e5cbe11).
Report is 30 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1498   +/-   ##
=======================================
  Coverage   91.46%   91.46%           
=======================================
  Files          54       54           
  Lines        7509     7511    +2     
  Branches      906      907    +1     
=======================================
+ Hits         6868     6870    +2     
  Misses        457      457           
  Partials      184      184           

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[gadomski]

Also needs a CHANGELOG entry.