Add icat5 endpoints

[Reillyhewitson]

This PR will close #373

Description

I have created models for ICAT5 entities as they were required to start the application, I have added the entities to the entity dictionary and added new entries to the postman collection so it is easy to try out the new enrpoints.

Testing Instructions

Add a set up instructions describing how the reviewer should test the code

• Review code
• Check GitHub Actions build
• If icatdb Generator Script Consistency Test CI job fails, is this because of a deliberate change made to the script to change generated data (which isn't actually a problem) or is here an underlying issue with the changes made?
• Review changes to test coverage
• Does this change mean a new patch, minor or major version should be made? If so, does one of the commit messages feature fix:, feat: or BREAKING CHANGE: so a release is automatically made via GitHub Actions upon merge?
• Ensure that Changes to tests so they pass with icat 5 #381 is merged first

Agile Board Tracking

Connect to #373

[codecov]

Codecov Report

Base: 94.48% // Head: 94.83% // Increases project coverage by +0.35% 🎉

Coverage data is based on head (6f10cb3) compared to base (4d6b066).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@                     Coverage Diff                     @@
##           feature/icat5-tests#374     #383      +/-   ##
===========================================================
+ Coverage                    94.48%   94.83%   +0.35%     
===========================================================
  Files                           39       39              
  Lines                         3116     3327     +211     
  Branches                       311      311              
===========================================================
+ Hits                          2944     3155     +211     
  Misses                         144      144              
  Partials                        28       28              

Impacted Files	Coverage Δ
...api/src/resources/entities/entity_endpoint_dict.py	100.00% <ø> (ø)
...gateway_api/src/datagateway_api/database/models.py	97.27% <100.00%> (+0.81%)	⬆️

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