PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines
• Tests for the changes have been added
• Docs have been added / updated

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.