Add flag to delete keys even if the user does not remember the password

[alessio]

Forked from #2923

Description:

As a gaiacli user
I want to forcibly remove a key from the store
So that I can delete key to which I forgot the passphrase

Acceptance criteria

Given a key name
When I run gaiacli keys --force <key>
Then the key is removed from the local store and I'm not prompted to input the password.

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[alessio]

This is useful in unattended execution scenario too.