fix(ldap-login): create custom serializer to fix login field

[gagantrivedi]

Thanks for submitting a PR! Please check the boxes below:

• I have added information to docs/ if required so people know about the feature!
• I have filled in the "Changes" section below?
• I have filled in the "How did you test this code" section below?
• I have used a Conventional Commit title for this Pull Request

Changes

• Add a custom login serializer to make login field configurable because LDAP supports login using username/password instead of email/password

How did you test this code?

Adds a unit test

[vercel]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

3 Skipped Deployments

Name	Status	Preview	Comments	Updated (UTC)
docs	⬜️ Ignored (Inspect)	Visit Preview		Aug 27, 2024 10:10am
flagsmith-frontend-preview	⬜️ Ignored (Inspect)	Visit Preview		Aug 27, 2024 10:10am
flagsmith-frontend-staging	⬜️ Ignored (Inspect)	Visit Preview		Aug 27, 2024 10:10am

[github-actions]

Docker builds report

Image	Build Status	Security report
ghcr.io/flagsmith/flagsmith-api-test:pr-4535	Finished ✅	Skipped
ghcr.io/flagsmith/flagsmith-frontend:pr-4535	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-api:pr-4535	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-private-cloud:pr-4535	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith:pr-4535	Finished ✅	Results ✅

[github-actions]

Uffizzi Preview deployment-55500 was deleted.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.98%. Comparing base (5e02eb4) to head (96640be).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4535      +/-   ##
==========================================
+ Coverage   96.94%   96.98%   +0.04%     
==========================================
  Files        1180     1180              
  Lines       39679    39682       +3     
==========================================
+ Hits        38467    38487      +20     
+ Misses       1212     1195      -17     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.