Add OIDC login

[ajkyffin]

This PR will close #135

Description

Adds endpoints for OIDC authentication

Still TODO:

• Add tests
• Add instructions to README.md

Testing Instructions

Add a set up instructions describing how the reviewer should test the code (will be done after updating README.md)

• Review code
• Check GitHub Actions build
• Review changes to test coverage
• Test using PKCE
• Test using a client_secret

[louise-davies]

When trying to run this branch in Docker (either via the image the CI built and uploaded to Harbor or building locally) I get an import error:

ImportError: cannot import name 'OIDC_ICATAuthenticator' from
'scigateway_auth.src.authentication'
(/app/scigateway_auth/src/authentication.py)

EDIT:
64a4b9a - this refactor wasn't completed in the imports, so I just added a commit to fix this

[ajkyffin]

Grrrr. Yes I broke it but I made the linter happy.

[codecov]

Codecov Report

❌ Patch coverage is 17.42424% with 109 lines in your changes missing coverage. Please review.
✅ Project coverage is 47.91%. Comparing base (bef86ae) to head (efb2f74).
⚠️ Report is 53 commits behind head on main.

Files with missing lines	Patch %	Lines
scigateway_auth/src/oidc.py	0.00%	57 Missing ⚠️
scigateway_auth/routers/authentication.py	0.00%	40 Missing ⚠️
scigateway_auth/src/authentication.py	27.27%	8 Missing ⚠️
scigateway_auth/common/config.py	82.60%	4 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #154       +/-   ##
===========================================
- Coverage   65.55%   47.91%   -17.64%     
===========================================
  Files           9       12        +3     
  Lines         360      480      +120     
  Branches       13        0       -13     
===========================================
- Hits          236      230        -6     
- Misses        124      250      +126     

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