Disable creation of classic pipelines

Introduced a feature to disable the creation of classic build and release pipelines. This feature enhances security by enforcing the use of YAML pipelines, which offer better security through code review, resource access management, and runtime parameters. The feature can be enabled at the organization or project level and impacts UI elements, REST APIs, and the creation of new classic pipelines, task groups, and deployment groups. Existing classic pipelines can still be edited and run.