(Closes #3435) Metatrans docs

[LonelyCat124]

This is the initial stage to have support for docs from _SUB_TRANSFORMATIONS supported.

There are remaining issues to fix:

1. No unit tests cover this code.
2. We can get repeated options which result in repeated docs:

>>> print(MaximalOMPParallelRegionTrans.apply.__doc__)
    Applies the transformation to the nodes provided.


    :param nodes: can be a single node, a schedule or a list of nodes.
    :param bool node_type_check: whether or not the type of the
        nodes enclosed in the region should be tested to avoid using
        unsupported nodes inside a region.
    :param bool node_type_check: (Option used for OMPParallelTrans) whether or not the type of the
        nodes enclosed in the region should be tested to avoid using
        unsupported nodes inside a region.

MaximalOMPParallelRegionTrans inherits the node_type_check from RegionTrans, but then also finds it imported from its SUB_TRANSFORMATION class. @sergisiso Do you think I should avoid repeated docstrings? Should it be limited in some way to only be if the strings are ==? I think I can do that check (as the "Option used for ...") is added later.

[codecov]

Codecov Report

❌ Patch coverage is 89.33333% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 99.95%. Comparing base (b45ff81) to head (5b174a3).

Files with missing lines	Patch %	Lines
src/psyclone/docstring_parser.py	84.61%	6 Missing ⚠️
src/psyclone/utils.py	88.23%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3438      +/-   ##
==========================================
- Coverage   99.96%   99.95%   -0.02%     
==========================================
  Files         391      391              
  Lines       54668    54728      +60     
==========================================
+ Hits        54649    54701      +52     
- Misses         19       27       +8     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.