feat(CommandInteraction): add toString method

[ImRodry]

Please describe the changes this PR makes and why it should be merged:
This PR adds a toString method to CommandInteraction that outputs a string that can be copied by a user in order to execute the same command again. There’s an upcoming update to the client text editor so I’m not sure how this will work once that’s out but this works fine at the moment

Example:

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)

[Jiralite]

1. Can we put this in the command interaction option resolver so context menu commands can utilise this too (as well as autocomplete when it is released)?
2. If nearly all the checks stem from the command interaction option resolver, you might as well move it into there and have this method call it from there. This can deduplicate code if you go with the aforementioned point.

[ImRodry]

• Can we put this in the command interaction option resolver so context menu commands can utilise this too (as well as autocomplete when it is released)?
• If nearly all the checks stem from the command interaction option resolver, you might as well move it into there and have this method call it from there. This can deduplicate code if you go with the aforementioned point.

1. No because context menus cannot be copied like application commands can. If they could I would’ve put this in BaseCommandInteraction
2. I don’t think that makes any sense because you’re stringifying the command and not the options, and you can also stringify a command with no options