add alternative executionUnit formats to support OGC-API schemas

[fmigneault]

changes

• Support alternative representations from OGC API - Processes schemas for executionUnit definition
  during Process deployment. The unit does not need to be nested under unit or a list anymore, and can instead
  be directly provided as JSON mapping. For backward compatibility, the previous list representation is still allowed
  (fixes Support new formats of executionUnit #507).
• Support an additional type property along a unit item describing an executionUnit to specify an IANA
  Media-Type that categories the unit contents, similarly to how it could be provided for its href counterpart.
  For the moment, only CWL-based unit are supported, but this could allow future extensions to provide alternate
  representations of an Application Package.

[codecov]

Codecov Report

Merging #574 (1767a00) into master (7413e61) will decrease coverage by 0.02%.
Report is 1 commits behind head on master.
The diff coverage is 94.11%.

❗ Current head 1767a00 differs from pull request most recent head e9957f7. Consider uploading reports for the commit e9957f7 to get more accurate results

@@            Coverage Diff             @@
##           master     #574      +/-   ##
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- Coverage   84.90%   84.88%   -0.02%     
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  Files          79       79              
  Lines       17935    17921      -14     
  Branches     2718     2718              
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- Hits        15227    15213      -14     
  Misses       1980     1980              
  Partials      728      728              

Files	Coverage Δ
weaver/wps_restapi/swagger_definitions.py	99.83% <100.00%> (-0.01%)	⬇️
weaver/processes/utils.py	80.00% <83.33%> (+0.14%)	⬆️

... and 2 files with indirect coverage changes