[Compose] - Implement slash commands support

[filbabic]

Context

We need to support the slash command logic in our composer, as other SDKs do.

Acceptance criteria

To accept this task we need to complete the following items:

• [ ] Add the logic to recognize the / (slash) symbol and prompt for commands.
• [ ] Show a list of available commands to the user, based on our existing options.
• [ ] Update the UI of the Composer in case the user picks a command. (e.g. remove integrations, show giphy).
• [ ] Perform the selected action if the conditions are fulfilled (e.g. banning users if the username is correct & we have the permissions)

[filbabic]

Closing this one since it's more less covered in #2629.

Will add a task to improve this UI/UX with more commands in the future, based on what we expose to our users.