hermes keys add and hermes keys restore are redundant

[greg-szabo]

Crate

relayer-cli

Summary

We could reduce the number of commands supported under hermes keys.

Problem Definition

With the --hd-path command implemented for both keys add and keys restore, the two commands essentially require the same parameters but in a different format. One requests the mnemonic from a file, the other from the stdin.

It would simpler to only maintain one code base instead.

Proposal

a.) Merge the two commands into add that has both the -f and the -m command. They are interchangeable but only one can be defined.
b.) Come up with other solutions so there's only one code that supports adding/restoring keys.

Acceptance Criteria

Done: The process of adding/restoring keys is straightforward.

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[mircea-c]

I'd like to add that the -m flag used in the restore command is very unsafe. The mnemonic has to be pasted in the command line and then is possibly saved to shell history file. I would eliminate this completely in favour of reading the mnemonics from a file or from stdin.