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

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.

tahowallet / extension