Update and clarify description, license, datetime properties

[tylanderson]

Related Issue(s):

• Fix docstring for license to indicate that it supports other as an option and no longer supports proprietary and various. #1377
• In common metadata: validate that if a description is provided it is not empty #1381
• Treat start_datetime and end_datetime as inclusive bounds #1382

Description:

A collection of smaller updates for STAC 1.1.0 with regard to description, license, and datetime. I grouped these together as they were small changes, but can broken down if that's preferred.

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 91.21%. Comparing base (ba406cb) to head (68b94ea).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1445   +/-   ##
=======================================
  Coverage   91.21%   91.21%           
=======================================
  Files          52       52           
  Lines        7237     7239    +2     
  Branches     1018     1019    +1     
=======================================
+ Hits         6601     6603    +2     
  Misses        457      457           
  Partials      179      179           

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