feat(CategoryChannel): add createChannel shortcut method

[ImRodry]

Please describe the changes this PR makes and why it should be merged:
This PR adds a method to CategoryChannel called createChannel that creates a channel inside that category. It also fixes a bug in the options interface to disallow GUILD_NEWS_THREAD types on both the GuildChannelCreateOptions and the CategoryCreateChannelOptions interfaces

Status and versioning classification:

• Code changes have been tested against the Discord API, or there are no code changes
• I know how to update typings and have done so, or typings don't need updating
• This PR changes the library's interface (methods or parameters added)

[vladfrangu]

Smallest nit, but can be merged without it so LGTM

[anandre]

I don't think that this method brings any needed utility to the library. Adding a method that AFAIK is only on managers to separate class seems like it's cluttering up the library for no good reason. All this does is add more to the library for the convenience of setting one value for the user. Recently, the library has been removing extraneous helper/utility methods, and this is going in exactly the opposite direction.

[ImRodry]

@anandre the methods the library has been recently removing are only ones that were unreliable and caused more hassles than they solved (e.g. typing-related properties and methods, User#presence, etc). This method is indeed a convenience and I recognize that it would be better to have a children manager, however, that cannot be done until v14. If the reviewers prefer we can hold this off and transform CategoryChannel#children into a manager later on, however I don't see why this couldn't be added personally as it is quite convenient (e.g. to be used with a CHANNEL option in a slash command where you'd be able to call the method directly instead of using the channel's ID in the manager's method) and seems to be getting some positive feedback too.

Along with that, methods like this exist all across the library e.g. GuildMember#setX that all call the GuildMember#edit method, and others on other classes too, so I don't see why this shouldn't be added