See #5957. CLI cmd to generate hashed password from cleartext password

[SimonUnge]

Proposed Changes

Add cli cmd that generates a valid hashed password according to configured rabbitmq algorithm
Addresses cli cmd part of #5957

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[lukebakken]

Thank you!

[michaelklishin]

@SimonUnge can you please rebase this PR?

[SimonUnge]

@SimonUnge can you please rebase this PR?

Done @michaelklishin

[michaelklishin]

We don't have to do this in this PR but one thing the community is guaranteed to ask for is support for password entry via standard input. See rabbitmqctl change_passowrd and rabbitmqctl add_user for examples of how we do it in other places.