Json optional data path

[christopher-wild]

Related to issue 187.

I think the best way to handle directly providing a Dataframe rather than a path to data is to treat the data_path as optional.

Which it already is, so this adds a check to assert that one of the methods for providing data has been done

[github-actions]

🦙 MegaLinter status: ✅ SUCCESS

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ PYTHON	black	26		0	1.26s
✅ PYTHON	pylint	26		0	4.77s

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[codecov]

Codecov Report

Merging #198 (e390c3e) into main (45cb719) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #198   +/-   ##
=======================================
  Coverage   95.22%   95.22%           
=======================================
  Files          20       20           
  Lines        1381     1383    +2     
=======================================
+ Hits         1315     1317    +2     
  Misses         66       66           

Impacted Files	Coverage Δ
...usal_testing/specification/metamorphic_relation.py	98.19% <ø> (ø)
causal_testing/json_front/json_class.py	98.82% <100.00%> (+0.01%)	⬆️

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[christopher-wild]

I wanted to update the docs to include this feature, then ended up writing a lot of extra JSON Frontend docs, which ideally should have been a separate PR..