Define Endpoints for Search API

[MRichards99]

This PR will close #257

Description

This PR defines endpoints which need to be implemented for the search API.

I've used the endpoint= argument for add_resource() to prevent naming collisions between endpoints. This was happening with endpoints like /datasets (DataGateway API endpoint) and /search_api/datasets even though they're actually different endpoints. Using endpoint= fixed this.

#256 isn't implemented yet so the search API endpoints are always created. Once the new config has been implemented, endpoint creation should respect the config and only create them when they are wanted by the user. I have also hardcoded the extension which should be changed to look up the relevant config value once #256 is closed.

To remember to resolve both TODOs, I have opened #283 to tackle these issues once #256 and #257 have been completed.

Testing Instructions

Run the API on this branch and ensure that you can send requests to each of the newly defined endpoints (e.g. /search_api/datasets) which return a 200 and a response body of null.

I was a little undecided on whether this needs a version bump or not. I've gone for feature because these changes do add in new endpoints, even if they are unimplemented. I would welcome an alternative view on this though, I'm not sure if a different (or even no) version bump is more appropriate.

• 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?

Agile Board Tracking

Connect to #257

[codecov]

Codecov Report

Merging #284 (896d3b8) into master (a2de545) will increase coverage by 1.14%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #284      +/-   ##
==========================================
+ Coverage   84.82%   85.97%   +1.14%     
==========================================
  Files          36       36              
  Lines        2584     2603      +19     
  Branches      207      208       +1     
==========================================
+ Hits         2192     2238      +46     
+ Misses        368      342      -26     
+ Partials       24       23       -1     

Impacted Files	Coverage Δ
datagateway_api/src/api_start_utils.py	89.47% <100.00%> (+2.10%)	⬆️
...agateway_api/src/resources/search_api_endpoints.py	83.87% <100.00%> (+83.87%)	⬆️
...tagateway_api/src/swagger/apispec_flask_restful.py	54.38% <0.00%> (+1.75%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update a2de545...896d3b8. Read the comment docs.

[VKTB]

Looks good and all the endpoints return null as expected. I feel as though a version bump is necessary though I am not sure which one should be used. Might be a good idea getting thoughts from others on this.