[CONTENT_UPDATE] Update OCP 3.11 `crwctl server:stop` instructions to explain use of UAT

Users following the documentation [1] find that 'crwctl server:stop' gives an error message:

.....
Scale "plugin registry" deployment to zero
Wait until Plugin registry pod is deleted
› Error: E_AUTH_REQUIRED - CodeReady Workspaces authentication is enabled and an access token need to be provided (flag --access-token).
› For instructions to retrieve a valid access token refer to https://www.eclipse.org/che/docs/che-6/authentication.html

[1] https://access.redhat.com/documentation/en-us/red_hat_codeready_workspaces/2.0/html-single/installation_guide/index#uninstalling-codeready-workspaces-after-crwctl-installation_uninstalling-codeready-workspaces