[CLI] Seed Phrase should be optionally visible

[sabau]

Summary

gaiacli keys add testtest
Currently returns Addresses, but the seed phrase is not visible anymore.

Problem Definition

The seed phrase should be part of the output.
Either enabled or disabled by default but who use the command should be able to choose if he wants to see it via a flag.
Voyager currently uses it to access the account.

Proposal

Would be great if the seed phrase will be part of the formatted output instead of printed separately, it will make automations cleaner

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[alexanderbez]

@sabau the functionality is still there. You can still see the seed/mnemonic with the --no-backup flag. Granted I think the UX is a bit confusing so we can work on that.