Issue #2907838 by heddn, nielsonm, thomasmurphy: Adding members to group in bulk

Closes #2907838

config/install/system.action.group_subscribe_user_action.yml

+langcode: en
+status: true
+dependencies:
+  module:
+    - user
+id: group_subscribe_user_action
+label: 'Subscribe users to a group'
+type: user
+plugin: group_subscribe_user_action
+configuration: {  }