sidecar: Use leader start and stop hook.

[runkecheng]

What type of PR is this?

/enhancement

Which issue(s) this PR fixes?

#447 set the default value of xenon metadata, this can avoid metadata being empty (operator may not work).

But the setting role label still needs to rely on operator, so xenon is best to set role label for itself.

Fixes #

What this PR does?

Summary:

Re-enable the hook of leader start and leader stop.

Special notes for your reviewer?