feat(permissions): add use_external_apps permission

[shiftinv]

Summary

discord/discord-api-docs@f092440

This also moves use_application_commands and use_embedded_activities from Permissions.text and .voice respectively into a new category, Permissions.apps, which was added to the Discord client UI recently and includes these three permissions.

While #1173 is the main user apps PR, this permission is completely independent of that implementation.

Checklist

• If code changes were made, then they have been tested
  • I have updated the documentation to reflect the changes
  • I have formatted the code properly by running pdm lint
  • I have type-checked the code by running pdm pyright
• 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)
• This PR is not a code change (e.g. documentation, README, ...)