add custom define discovery

[gy09535]

Which issue(s) this PR fixes:

Fixes #4259

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[gy09535]

according to #4260

[nobodyiam]

Thanks, would you please also add some instructions so that other users could know how to use this discovery mode? we may put it after zookeeper discovery in distributed-deployment-guide.

[gy09535]

Thanks, would you please also add some instructions so that other users could know how to use this discovery mode? we may put it after zookeeper discovery in distributed-deployment-guide.

added

[nobodyiam]

LGTM