feat: add linked accounts page (#883)

* feat(linked-accounts): create page and display linked media server accounts

* feat(dropdown): add new shared Dropdown component

Adds a shared component for plain dropdown menus, based on the headlessui Menu component. Updates
the `ButtonWithDropdown` component to use the same inner components, ensuring that the only
difference between the two components is the trigger button, and both use the same components for
the actual dropdown menu.

* refactor(modal): add support for configuring button props

* feat(linked-accounts): add support for linking/unlinking jellyfin accounts

* feat(linked-accounts): support linking/unlinking plex accounts

* fix(linked-accounts): probibit unlinking accounts in certain cases

Prevents the primary administrator from unlinking their media server account (which would break
sync). Additionally, prevents users without a configured local email and password from unlinking
their accounts, which would render them unable to log in.

* feat(linked-accounts): support linking/unlinking emby accounts

* style(dropdown): improve style class application

* fix(server): improve error handling and API spec

* style(usersettings): improve syntax & performance of user password checks

* style(linkedaccounts): use applicationName in page description

* fix(linkedaccounts): resolve typo

* refactor(app): remove RequestError class

overseerr-api.yml

@@ -4423,6 +4423,104 @@ paths:
       responses:
         '204':
           description: User password updated
+  /user/{userId}/settings/linked-accounts/plex:
+    post:
+      summary: Link the provided Plex account to the current user
+      description: Logs in to Plex with the provided auth token, then links the associated Plex account with the user's account. Users can only link external accounts to their own account.
+      tags:
+        - users
+      parameters:
+        - in: path
+          name: userId
+          required: true
+          schema:
+            type: number
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              type: object
+              properties:
+                authToken:
+                  type: string
+              required:
+                - authToken
+      responses:
+        '204':
+          description: Linking account succeeded
+        '403':
+          description: Invalid credentials
+        '422':
+          description: Account already linked to a user
+    delete:
+      summary: Remove the linked Plex account for a user
+      description: Removes the linked Plex account for a specific user. Requires `MANAGE_USERS` permission if editing other users.
+      tags:
+        - users
+      parameters:
+        - in: path
+          name: userId
+          required: true
+          schema:
+            type: number
+      responses:
+        '204':
+          description: Unlinking account succeeded
+        '400':
+          description: Unlink request invalid
+        '404':
+          description: User does not exist
+  /user/{userId}/settings/linked-accounts/jellyfin:
+    post:
+      summary: Link the provided Jellyfin account to the current user
+      description: Logs in to Jellyfin with the provided credentials, then links the associated Jellyfin account with the user's account. Users can only link external accounts to their own account.
+      tags:
+        - users
+      parameters:
+        - in: path
+          name: userId
+          required: true
+          schema:
+            type: number
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              type: object
+              properties:
+                username:
+                  type: string
+                  example: 'Mr User'
+                password:
+                  type: string
+                  example: 'supersecret'
+      responses:
+        '204':
+          description: Linking account succeeded
+        '403':
+          description: Invalid credentials
+        '422':
+          description: Account already linked to a user
+    delete:
+      summary: Remove the linked Jellyfin account for a user
+      description: Removes the linked Jellyfin account for a specific user. Requires `MANAGE_USERS` permission if editing other users.
+      tags:
+        - users
+      parameters:
+        - in: path
+          name: userId
+          required: true
+          schema:
+            type: number
+      responses:
+        '204':
+          description: Unlinking account succeeded
+        '400':
+          description: Unlink request invalid
+        '404':
+          description: User does not exist
   /user/{userId}/settings/notifications:
     get:
       summary: Get notification settings for a user