OIDC Dev Service: Support 'client_secret_basic' client authentication

[michalvavrik]

• closes: OIDC Dev Service invalid_request for when client secret is set #47301
• please note that I didn't document the support, this PR fixes the reported issue (support for the client_secret_basic), but I think more work needs to be done before we declare support for using OIDC Dev Service with OIDC Client and I plan to do that work very soon

[quarkus-bot]

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