Support for injecting an authorization token

[moritzschmitz-oviva]

What this PR does / why we need it:
What: This PR enables support for using an existing authorization token.
Why: This helps in scenarios where the token isn't issued by Keycloak, but only verified by it.

Special notes for your reviewer:
We have a special use-case where all admin accounts need to have enabled 2FA because our /admin is publicly accessible (and needs to be). We are using https://spiffe.io/ in our cluster to issue identities to our backend components. Being able to use the KeycloakBuilder functionality of injecting an authorization token would allow us to leverage the same capabilities.

PR Readiness Checklist:

Complete these before marking the PR as ready to review:

• the CHANGELOG.md release notes have been updated to reflect any significant (and particularly user-facing) changes introduced by this PR

[codecov]

Codecov Report

Attention: Patch coverage is 53.84615% with 6 lines in your changes are missing coverage. Please review.

Project coverage is 95.49%. Comparing base (554c4a1) to head (3cbc12d).

❗ Current head 3cbc12d differs from pull request most recent head 2ca1456. Consider uploading reports for the commit 2ca1456 to get more accurate results

Files	Patch %	Lines
...sys/keycloak/config/provider/KeycloakProvider.java	45.45%	2 Missing and 4 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #981      +/-   ##
============================================
- Coverage     95.56%   95.49%   -0.08%     
+ Complexity     1370     1364       -6     
============================================
  Files            81       80       -1     
  Lines          4400     4375      -25     
  Branches        500      493       -7     
============================================
- Hits           4205     4178      -27     
- Misses           94       98       +4     
+ Partials        101       99       -2     

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[sonarcloud]

Quality Gate passed

Kudos, no new issues were introduced!

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See analysis details on SonarCloud

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarCloud