Context menu, checks, and cooldowns guide

[Aryathel]

Summary

Updating the Context Menus guide (Just something I threw together as it is already being worked on by another as well). I plan to also specifically add an app_commands.checks guide, which will include information on cooldowns.

Checklist

• [ ] If code changes were made then they have been tested.
  • [ ] I have updated the documentation to reflect the changes.
• [ ] This PR fixes an issue.
• [ ] This PR adds something new (e.g. new method or parameters).
• [ ] This PR is a breaking change (e.g. methods or parameters removed/renamed)
• [x] This PR is not a code change (e.g. documentation, README, ...)

[Aryathel]

Added the checks guide, which includes the information on cooldowns. This guide is specifically for AppCommand checks, as there are differences from standard checks. Not sure if it deserves its own page, but the document is written up now and can be put wherever later.

[Aryathel]

Great job!

Thanks for catching stuff I missed!

[No767]

Just did a quick scan of this PR. Global interaction checks are not documented yet, which I will probably do in a bit

[Soheab]

~~This is missing the integration "checks" (default_permissions, nsfw, guild_only, etc).~~ did this as a comment for some reason lol but they have been added.