fix: remove email requirement for the user, and use the username if no email provided (#900)

* fix: remove email requirement for the user, and use the username if no email provided

* fix: update translations

* fix: remove useless console.log

* test: fix user list test

* fix: disallow Plex users from changing their email

src/i18n/locale/en.json

@@ -1111,7 +1111,6 @@
   "components.UserList.creating": "Creating…",
   "components.UserList.deleteconfirm": "Are you sure you want to delete this user? All of their request data will be permanently removed.",
   "components.UserList.deleteuser": "Delete User",
-  "components.UserList.displayName": "Display Name",
   "components.UserList.edituser": "Edit User Permissions",
   "components.UserList.email": "Email Address",
   "components.UserList.importedfromJellyfin": "<strong>{userCount}</strong> {mediaServerName} {userCount, plural, one {user} other {users}} imported successfully!",
@@ -1145,9 +1144,11 @@
   "components.UserList.userdeleteerror": "Something went wrong while deleting the user.",
   "components.UserList.userfail": "Something went wrong while saving user permissions.",
   "components.UserList.userlist": "User List",
+  "components.UserList.username": "Username",
   "components.UserList.users": "Users",
   "components.UserList.userssaved": "User permissions saved successfully!",
-  "components.UserList.validationEmail": "You must provide a valid email address",
+  "components.UserList.validationEmail": "Email required",
+  "components.UserList.validationUsername": "You must provide an username",
   "components.UserList.validationpasswordminchars": "Password is too short; should be a minimum of 8 characters",
   "components.UserProfile.ProfileHeader.joindate": "Joined {joindate}",
   "components.UserProfile.ProfileHeader.profile": "View Profile",