Release leader election lock on shutdown

[mcristina422]

        // ReleaseOnCancel should be set true if the lock should be released
	// when the run context is cancelled. If you set this to true, you must
	// ensure all code guarded by this lease has successfully completed
	// prior to cancelling the context, or you may have two processes
	// simultaneously acting on the critical path.

[mwielgus]

/lgtm
/approve

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