Improvements for linksmith inventory and linksmith anansi

[amotl]

• Inventory: Accept linksmith inventory without INFILES argument
• Inventory: Improve pre-flight checks
• Anansi: Manage project list in YAML file curated.yaml, not Python
• Anansi: Provide anansi list-projects subcommand
• Anansi: Fix sort order of index file, use "by name asc/by version desc"
• Anansi: Accept --threshold option, forwarding to sphobjinv
• Anansi: Discover objects.inv also from RTD and PyPI
• Chore: Activate test case test_multiple_inventories_url
• Chore: Remove support for Python 3.7 and 3.8

[codecov]

Codecov Report

Attention: Patch coverage is 99.30556% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 99.77%. Comparing base (ec32922) to head (3f41714).

Files	Patch %	Lines
linksmith/sphinx/util.py	97.77%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##              main       #7      +/-   ##
===========================================
- Coverage   100.00%   99.77%   -0.23%     
===========================================
  Files           10       11       +1     
  Lines          316      440     +124     
===========================================
+ Hits           316      439     +123     
- Misses           0        1       +1     

Flag	Coverage Δ
unittests	99.77% <99.30%> (-0.23%)	⬇️

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