✨ Make leader election resourcelock configurable

[timebertt]

This PR makes the leader election resource lock configurable via manager.Options.LeaderElectionResourceLock.
It can be set to one of the lock types supported by client-go (ref):

• endpoints
• configmaps
• leases
• endpointsleases
• configmapsleases

It keeps the default of configmapsleases introduced by #1144, but allows folks to explicitly configure other LE strategies.

Fixes #460

/assign @alvaroaleman

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[timebertt]

/assign @pwittrock

[alvaroaleman]

/lgtm
/approve

Thanks @timebertt !

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: alvaroaleman, timebertt

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