Support for OIDC Client Credentials Flow in RESTClientJob

Current Situation

• The RESTClientJob supports Basic authentication,.
• The request body cannot be sent in application/x-www-form-urlencoded format.

Desired Behavior

• The RESTClientJob should support the Client Credentials Flow.
• The request body should be sent in application/x-www-form-urlencoded format using the urlEncodedData key instead of the body key in the request JSON.
• Sensitive information such as the Client ID and Client Secret can be specified from variables holding encrypted values. Related request headers can reference variables using the syntax %{client_id} and %{client_secret} if variables with this name exist and hold encrypted values, see JITL-763.