Add signup URL to authconfig payload

[alexeykazakov]

Required for #438
There is a new redirect page in that PR ^^^ which is supposed to do the following:

• it loads the authconfig from /api/v1/authconfig
• then if the user is not logged in already then it redirects the user to SSO for login
• then it checks if the user has already signed up. If not then the page redirects the user to the signup page.

This PR adds the signup URL (we store it as registrationServiceURL in the configuration) to the authconfig payload, so it's available to the clients in the last step above.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.46%. Comparing base (cbd0f40) to head (36c1237).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #464   +/-   ##
=======================================
  Coverage   79.45%   79.46%           
=======================================
  Files          42       42           
  Lines        2726     2727    +1     
=======================================
+ Hits         2166     2167    +1     
  Misses        471      471           
  Partials       89       89           

Flag	Coverage Δ
unittests	79.46% <100.00%> (+<0.01%)	⬆️

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[ranakan19]

Looks good!

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: alexeykazakov, MatousJobanek, ranakan19

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