Add a task in acceptance-tests pipeline to uninstall the operator

Currently, the acceptance-tests pipeline consists of a task to install the operator but it does not contain any task to uninstall the operator. If the tests have to be run on the same cluster with a different build, the user has to uninstall the operator first and then again have to retrigger the acceptance-tests pipeline

Acceptance Criteria:

• Test case to uninstall the operator is up to date in release-tests repo
• A task to uninstall the operator is present in the plumbing repo and its part of acceptance-tests pipeline