Changing image reference in any cluster task makes it unsupportable so those params should not be exposed.

Customers who need to run an operator-provided cluster task with their own custom image need to create a copy of a task.

Acceptance criteria:

• buildah task doesn't expose "BUILDER_IMAGE" param
• git-clone task doesn't expose "gitInitImage" param
• kn task doesn't expose "kn-image" param
• kn-apply task doesn't expose "KN_IMAGE" param
• maven task doesn't expose "MAVEN_IMAGE" param
• s2i-* tasks don't expose "BUILDER_IMAGE" param
• tkn task doesn't expose "TKN_IMAGE" param