Add option to disable provisioning new users via google login

[knolleary]

Part of #6484

Currently, the google social login flow will always automatically create a new user if they are logging in for the first time.

If we disable self-service sign-up of the app, we also need to prevent the social login from provisioning new users.

This adds a new admin option for the social login as to whether new users should be created when attempting to login for the first time.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.41%. Comparing base (01cfe8a) to head (819eb11).
⚠️ Report is 12 commits behind head on main.

Files with missing lines	Patch %	Lines
forge/ee/routes/sso/social/google.js	0.00%	2 Missing ⚠️
forge/routes/api/settings.js	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6485      +/-   ##
==========================================
- Coverage   76.42%   76.41%   -0.02%     
==========================================
  Files         396      396              
  Lines       19885    19888       +3     
  Branches     4766     4767       +1     
==========================================
  Hits        15198    15198              
- Misses       4687     4690       +3     

Flag	Coverage Δ
backend	76.41% <0.00%> (-0.02%)	⬇️

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[cstns]

Should we "link" this platform option to the existing Allow new users to register on the login screen option and offer the possibility of enablement only if the first option is also enabled?

I assume this is mostly intended for FFC so not sure how much we want to complicate things or if a change request to enable is required.

[knolleary]

Lets not complicate it for now. We're the only ones using these options.