PLT-7111 Add groupmsg command (#7419)

* Coping command_msg to use as command_groupmsg base

* Changing msg to groupmsg names in groumsg command

* Add groupmsg command

i18n/en.json

@@ -819,6 +819,57 @@
     "id": "api.command_msg.success",
     "translation": "Messaged user."
   },
+  {
+    "id": "api.command_groupmsg.desc",
+    "translation": "Sends a Group Message to the specified users"
+  },
+  {
+    "id": "api.command_groupmsg.group_fail.app_error",
+    "translation": "An error occurred while creating the group message."
+  },
+  {
+    "id": "api.command_groupmsg.fail.app_error",
+    "translation": "An error occurred while messaging the users."
+  },
+  {
+    "id": "api.command_groupmsg.invalid_user.app_error",
+    "translation": {
+      "one": "We couldn't find the user: {{.Users}}",
+      "other": "We couldn't find the users: {{.Users}}"
+    }
+  },
+  {
+    "id": "api.command_groupmsg.invalid_users.app_error",
+    "translation": "We couldn't find the users: %s"
+  },
+  {
+    "id": "api.command_groupmsg.min_users.app_error",
+    "translation": "Group messages are limited to a minimun of {{.MinUsers}} users."
+  },
+  {
+    "id": "api.command_groupmsg.max_users.app_error",
+    "translation": "Group messages are limited to a maximum of {{.MaxUsers}} users."
+  },
+  {
+    "id": "api.command_groupmsg.hint",
+    "translation": "@[username1],@[username2] 'message'"
+  },
+  {
+    "id": "api.command_groupmsg.list.app_error",
+    "translation": "An error occurred while listing users."
+  },
+  {
+    "id": "api.command_groupmsg.missing.app_error",
+    "translation": "We couldn't find the user"
+  },
+  {
+    "id": "api.command_groupmsg.name",
+    "translation": "message"
+  },
+  {
+    "id": "api.command_groupmsg.success",
+    "translation": "Messaged users."
+  },
   {
     "id": "api.command_offline.desc",
     "translation": "Set your status offline"