Update node-saml to 5

[knolleary]

Replaces #4734

The bump to node-saml@5 includes a breaking change on its options object - cert is now idpCert.

This PR updates to node-saml@5 and maps the old property to the new name. Tested locally against azure SSO.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.41%. Comparing base (efc15ce) to head (88cdfe2).
Report is 5 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5037   +/-   ##
=======================================
  Coverage   78.40%   78.41%           
=======================================
  Files         329      329           
  Lines       15478    15480    +2     
  Branches     3574     3574           
=======================================
+ Hits        12136    12138    +2     
  Misses       3342     3342           

Flag	Coverage Δ
backend	78.41% <100.00%> (+<0.01%)	⬆️

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[hardillb]

Tested with keycloak, appears to work as expected