Add flag to control the addition of 1Password buttons

[hassaansaleh]

Description

This PR adds a new flag enableOnePassword to WordPressAuthenticatorConfiguration. This flag controls the addition of 1Password buttons to the UI.
I also refactored OnePasswordFacade to make it more testable.

References: wordpress-mobile/WordPress-iOS#17516
This is the second PR that tackles this issue. Planned PRs:

• Cleanup unreachable code Remove unreachable code related to 1Password #623
• Remove 1Password button from UI when corresponding config is disabled (This PR)
• Configure all textfields to display Apple's native Password Autofill.

Screenshots

Screen	Before	After
LoginEmailViewController
LoginSelfHostedViewController
LoginUsernamePasswordViewController
LoginWPComViewController

No changes in GetStartedViewController, PasswordViewController or SiteCredentialsViewController.

Testing

I added unit tests to ensure that OnePasswordFacade's computed variable isOnePasswordEnabled - which controls that addition of 1Password buttons - considers both the new flag and 1Password availability.

To test this use the WordPress iOS PR. You need to test on a real device that has 1Password installed.

What to test

1. Check that 1Password's button is not added in any screen, unified UI and old UI.
2. Enable one password by changing flag's value in WordPressAuthenticationManager and verify that the old behavior is maintained.

Associated PRs

WordPress iOS PR: wordpress-mobile/WordPress-iOS#17596

[hassaansaleh]

Closing this as we decided to remove 1Password completely
Check #626