Leadership transfer cmd

[dhiaayachi]

This is an attempt to implement a command that would trigger a raft leadership transfer. The idea about this trace back to a customer issue where we needed to trigger leader transfer to be able to upgrade a leader node.

This dependent to a change in raft that fix some of the gaps in leadership transfer, those gaps would make the transfer fail. https://github.com/hashicorp/raft/pull/487

I made an attempt in naming the sub command but open to any suggestions.

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5 out of 6 committers have signed the CLA.

• [x] hc-github-team-consul-core
• [x] andrewstucki
• [x] boruszak
• [x] dhiaayachi
• [x] claire-labry
• [ ] FFMMM

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[dhiaayachi]

Closed in favour of https://github.com/hashicorp/consul/pull/14132