Add the ability for users to change their Tally Ho password.

[0xDaedalus]

Requirements:

• [ ] Add an ALLOW_CHANGE_PASSWORD feature flag and gate the following functionality behind it.
• [ ] Add unit tests for any added methods in keyring service.
• [ ] Add functionality to keyring service that allows a caller to encrypt unlocked vaults with a newly designated passphrase.
• [ ] Add a "Change Password" option to Settings.tsx with formatting similar to the Bug Report option.
• [ ] Add a dedicated page for changing a users password. This page should:
  • [ ] require users to re-enter their password to access it even if the extension is unlocked (probably via the typical lock screen).
  • [ ] Use the PasswordStrengthBar
  • [ ] Require the user to enter their new password twice and confirm that the entries match
• [ ] Remove the copy about not being able to change passwords from the initial password creation flow.

Notes:

• It might be a good idea to modify and reuse the existing KeyringSetPassword component for the Change Password screen.
• Adding unit / integration tests are heavily encouraged while developing feature as it is security-sensitive and not likely to change much once implemented.
• The users password is never (and should never be) persisted. Password verification happens here and will fail if a given password attempting to decrypt a vault does not match the password used to encrypt it.

[rgdalessandro]

I have picked up this issue and have started working on it.