[Feature]: Pass keyring encryption passphrase via file

[ljk662]

Summary

Instead of needing to pass in the encryption passphrase via std-input, create a flag that lets users pass in the passphrase via a file. This will make importing keys (and listing keys) in the keyring easier and more secure in a scripting setting.

Problem Definition

n/a

Proposed Feature

Make a flag to pass keyring encryption passphrase via a file.

[ljk662]

Hey, thanks for implementing so fast!!

Unfortunately, this isn't exactly what I meant. I was hoping to enter the encryption passphrase thats used when you use keyring-backend-file that is asked anytime you do something like gaiad keys list or gaiad keys show.

[ljk662]

@hieuvubk