[MM-9904] Add /invite slash command to invite users to a channel (#8482)

* [MM-9904] Add /invite slash command to invite users to a channel

* Update en.json

i18n/en.json

@@ -814,6 +814,54 @@
     "id": "api.command_join.success",
     "translation": "Joined channel."
   },
+  {
+    "id": "api.command_invite.hint",
+    "translation": "@[username] ~[channel]"
+  },
+  {
+    "id": "api.command_invite.name",
+    "translation": "invite"
+  },
+  {
+    "id": "api.command_invite.desc",
+    "translation": "Invite a user to a channel"
+  },
+  {
+    "id": "api.command_invite.missing_message.app_error",
+    "translation": "Missing Username and Channel."
+  },
+  {
+    "id": "api.command_invite.missing_user.app_error",
+    "translation": "We couldn't find the user."
+  },
+  {
+    "id": "api.command_invite.channel.app_error",
+    "translation": "Error to retrieve the current channel."
+  },
+  {
+    "id": "api.command_invite.channel.error",
+    "translation": "Could not find the channel {{.Channel}}. Please use the [channel handle](https://about.mattermost.com/default-channel-handle-documentation) to identify channels."
+  },
+  {
+    "id": "api.command_invite.fail.app_error",
+    "translation": "An error occurred while joining the channel."
+  },
+  {
+    "id": "api.command_invite.permission.app_error",
+    "translation": "You don't have enough permissions to add {{.User}} in {{.Channel}}."
+  },
+  {
+    "id": "api.command_invite.directchannel.app_error",
+    "translation": "You can't add someone to a direct message channel."
+  },
+  {
+    "id": "api.command_invite.user_already_in_channel.app_error",
+    "translation": "{{.User}} is already in the channel."
+  },
+  {
+    "id": "api.command_invite.success",
+    "translation": "{{.User}} added to {{.Channel}} channel."
+  },
   {
     "id": "api.command_kick.name",
     "translation": "kick"