UI: Fix styling for username input when editing a user

[malinac02]

Fix styling for username input when editing a user

Description:

• With the userpass auth method, you can't edit an already existing username. If you click in the username input field, it is not editable. The problem was that the username input field looks editable due to its styling
• Fix: Now the username field has styling so that it looks non editable
• Note: The username input field is a readonly field. The original goal was to make this field look identical to a disabled input, but I spoke with design and the readonly field should instead look like the screenshot below. (In other words, this now looks different than the design in the Jira ticket!)
• How to see this:
  • Access > Authentication Methods > Enable new method > Username & password
  • Create and save a new user
  • Edit the user
  • The username cannot be edited, and the styling matches that

Images:
Before:

After: