Align keycloak typings

[kcinay055679]

PR Checklist

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• The commit message follows our guidelines
• Tests for the changes have been added
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PR Type

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

The current typings for provideKeycloak do not allow passing a string URL as the config value, even though this usage is supported at runtime.

Issue Number: #657

What is the new behavior?

Updates the typings to allow string URLs to be used as the config value in provideKeycloak, for example:

provideKeycloak({ config: '/keycloak.json' });

Adds/updates tests to cover this behavior.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

This change aligns the typings with the existing runtime behavior.

[kcinay055679]

this is a one on one copy of DaSchTour#2
i tried to add the funcionality to pass an Observable (or a Promise or anything similar for that matter) but this would only make everything much more complicated, so i think just adding the URL is the most pragmatic solution, even if the pr is vibe coded