Modify invite link for SSO enabled external users

[knolleary]

Closes #4784

When inviting an external user on an SSO-enabled domain with auto-create enabled, the invite text will now link to the login page rather than create-account.

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 78.79%. Comparing base (2fc508e) to head (d4318e2).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
forge/routes/api/teamInvitations.js	80.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4786   +/-   ##
=======================================
  Coverage   78.79%   78.79%           
=======================================
  Files         311      311           
  Lines       14782    14787    +5     
  Branches     3385     3387    +2     
=======================================
+ Hits        11647    11651    +4     
- Misses       3135     3136    +1     

Flag	Coverage Δ
backend	78.79% <80.00%> (+<0.01%)	⬆️

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