Add setting to disable new user registration on self-hosted instances (#1163)

* Add clipboard stimulus controller

* Add invite codes controller

* Setting to force invite code for new signups

* Fix erb linter

* Normalize keys

* Add POST /invite_codes

* Cleanup clipboard_controller.js

* Create invite codes on-demand

* Design changes

* Style alignment

* Update app/views/invite_codes/_invite_code.html.erb

Co-authored-by: Zach Gollwitzer <zach.gollwitzer@gmail.com>
Signed-off-by: Tony Vincent <tonyvince7@gmail.com>

* Update app/views/invite_codes/_invite_code.html.erb

Co-authored-by: Zach Gollwitzer <zach.gollwitzer@gmail.com>
Signed-off-by: Tony Vincent <tonyvince7@gmail.com>

* Split into individual forms

* Fix missing styles

* Update app/javascript/controllers/clipboard_controller.js

Co-authored-by: Zach Gollwitzer <zach.gollwitzer@gmail.com>
Signed-off-by: Tony Vincent <tonyvince7@gmail.com>

* Fix test

---------

Signed-off-by: Tony Vincent <tonyvince7@gmail.com>
Co-authored-by: Zach Gollwitzer <zach.gollwitzer@gmail.com>

config/locales/views/invite_codes/en.yml

@@ -0,0 +1,7 @@
+---
+en:
+  invite_codes:
+    index:
+      invite_code_description: Generate a new code to see it displayed here. Generated
+        codes that have been used will no longer be shown.
+      no_invite_codes: No codes to show

config/locales/views/settings/en.yml

@@ -12,6 +12,13 @@ en:
         email_sender: Email Sender
         email_sender_placeholder: user@mydomain.com
         general_settings_title: General Settings
+        invite_settings:
+          generate_tokens: Generate new code
+          generated_tokens: Generated codes
+          invite_code_description: Every new user that joins your instance if Maybe
+            can only do so via an invite code
+          require_invite_for_signup: Require invite code for new sign ups
+          title: Invite Codes
         page_title: Self-Hosting
         provider_settings:
           title: Provider Settings