Send parent_id when a thread is selected through slash commands

[ghost]

Description

Currently the CHANNEL option type accepts threads, if a user selects a thread it doesn't send the thread's parent_id property. And there is no way to identify the parent channel of the thread.

Why this is needed

This offers a way to do some checks on the parent channel. In my case I wanted to check if the user and the bot had specific permissions in the parent channel.

[devsnek]

parent_id and thread_metadata will be present after the next api deploy.