feat(plex): selective user import (#2188)

* feat(api): allow importing of only selected Plex users

* feat(frontend): modal for importing Plex users

* feat: add alert if 'Enable New Plex Sign-In' setting is enabled

* refactor: fetch all existing Plex users in a single DB query

Co-authored-by: Ryan Cohen <ryan@sct.dev>

src/i18n/globalMessages.ts

@@ -31,6 +31,8 @@ const globalMessages = defineMessages({
   testing: 'Testing…',
   save: 'Save Changes',
   saving: 'Saving…',
+  import: 'Import',
+  importing: 'Importing…',
   close: 'Close',
   edit: 'Edit',
   areyousure: 'Are you sure?',