Bugfix/include distinct requests #211

[MRichards99]

This PR will close #211

Description

This fixes a bug found when making an e2e test pass on DataGateway regarding included attributes on a distinct filter (linked issue has more details about this). I added some unit tests for this work, to test that this functionality works as intended (test_prepare_distinct_fields()). I increased test coverage a bit too - test_valid_distinct_attribute_mapping(), test_invalid_distinct_attribute_mapping() and changes in test_session_handling.py.

There's some dependency updates, as safety is requesting they be updated for the CI to pass.

Testing Instructions

For the request shown in the issue, this is the correct response (assuming the API is pointing at preprod's ICAT):

[
    {
        "dataset": {},
        "id": 30
    }
]

• Review code
• Check GitHub Actions build
• Review changes to test coverage
• Test that included/related entity attributes can be used on a distinct filter and return the correct response

Agile Board Tracking

Connect to #211

[codecov]

Codecov Report

Merging #212 (02778a2) into master (04eafd5) will increase coverage by 0.60%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #212      +/-   ##
==========================================
+ Coverage   86.94%   87.55%   +0.60%     
==========================================
  Files          28       28              
  Lines        2229     2233       +4     
  Branches      193      194       +1     
==========================================
+ Hits         1938     1955      +17     
+ Misses        250      241       -9     
+ Partials       41       37       -4     

Impacted Files	Coverage Δ
datagateway_api/common/icat/query.py	84.68% <100.00%> (+8.98%)	⬆️
...i/src/resources/non_entities/sessions_endpoints.py	100.00% <0.00%> (+16.00%)	⬆️

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