Allow a previously reset node to rejoin its original cluster (backport #13643) (backport #13667)

[mergify]

If a cluster member for whatever reason gets its local state wiped, it has a hard time re-joining the cluster, as the old cluster members will think the node is already a member and reject the request (if mnesia is used).

Proposed Changes

Mnesia: On failure due to 'already a member', ask to leave the cluster first and retry.
Khepri: no-op. Khepri is less strict already, and rabbit_khepri:can_join would accept a join request from a node that is already a member

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Further Comments

I would like early feedback here, as to if this naive approach is even OK, if there should be a limited set of retries, and if the logic should live in rabbit_mnesia or in rabbit_db_cluster?
It feels a bit wonky that a function called can_join_cluster would also try to leave a cluster and try again, so perhaps it would be better if rabbit_db_cluster:join instead initiates the leave and retry request?

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This is an automatic backport of pull request #13643 done by [Mergify](https://mergify.com).

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This is an automatic backport of pull request #13667 done by [Mergify](https://mergify.com).