Add custom Weaver schema definitions for CWL

[fmigneault]

Description

Avoids warnings about "unknown hints" when loading custom CWL requirements for remote process references.
Previously, custom requirements would have to be loaded as hints since they were not technically defined.
With this change, they would be also valid using explicit requirements.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.28%. Comparing base (c21b031) to head (670c821).

❗ Current head 670c821 differs from pull request most recent head 96e06b8. Consider uploading reports for the commit 96e06b8 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #529      +/-   ##
==========================================
- Coverage   85.71%   84.28%   -1.44%     
==========================================
  Files          79       78       -1     
  Lines       18585    16854    -1731     
  Branches     2847     2562     -285     
==========================================
- Hits        15930    14205    -1725     
- Misses       1916     1952      +36     
+ Partials      739      697      -42     

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