feat:add transfer Leader cmd

[E2ern1ty]

What type of PR is this?

• bug
• feature
• enhancement

What problem(s) does this PR solve?

Issue(s) number:

Description:

I think this feature will be more universal if placed in the nebula kernel
vesoft-inc/nebula-operator#270

How do you solve it?

add new transfer cmd for nebula, remove leader before change storaged group.
Maybe this function needs some guidance to make it better.

Special notes for your reviewer, ex. impact of this fix, design document, etc:

test in 3 replica,2 shards,just as the picture:

Checklist:

Tests:

• Unit test(positive and negative cases)
• Function test
• Performance test
• N/A

Affects:

• Documentation affected (Please add the label if documentation needs to be modified.)
• Incompatibility (If it breaks the compatibility, please describe it and add the label.）
• If it's needed to cherry-pick (If cherry-pick to some branches is required, please label the destination version(s).)
• Performance impacted: Consumes more CPU/Memory

Release notes:

Please confirm whether to be reflected in release notes and how to describe:

ex. Fixed the bug .....