keycloak: add support for client_credentials authentication (#10231)
* add client_credentials authentication for keycloak tasks incl. test case
* support client credentials in all keycloak modules
* Add changelog fragment
* fix typos in required list
* Update changelogs/fragments/10231-keycloak-add-client-credentials-authentication.yml
* revert keycloak url in test environment
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(cherry picked from commit f44ca23d7a)
Co-authored-by: divinity666 <65871511+divinity666@users.noreply.github.com>
Co-authored-by: Felix Fontein <felix@fontein.de>
