Add support to `jsk sync` for clearing application commands

[clari7744]

Usage remains largely the same, but prefixing a target with - will switch to upserting an empty payload - alone or -$ can both be used to clear global commands -., -*, or -{guild_id} all simply clear the commands for the expected target

Rationale

Currently, if I want to clear my commands (my use case, btw, is clearing from the beta bot so they don't interfere with the public bot), I have to manually type bot.tree.clear_commands(guild=guild/None), so this just makes it easier to wipe commands from a locale.

On a similar note, I wanted to also ask - thoughts on a way to replicate

CommandTree.copy_global_to(guild=guild)
await CommandTree.sync(guild=guild)

with jsk sync? I was thinking something like +{target} could handle that for guild ids/*/., and be ignored for $?

Summary of changes made

I created a second set that holds the guilds to be cleared, and changed the cleaned guilds list to be a tuple of [id, clear?], then loop through and set payload to an empty list when clear is True

Checklist

• [x] This PR changes the jishaku module/cog codebase
  • [x] These changes add new functionality to the module/cog
  • [ ] These changes fix an issue or bug in the module/cog
  • [x] I have tested that these changes work on a production bot codebase
  • [x] I have tested these changes against the CI/CD test suite
  • [ ] I have updated the documentation to reflect these changes
• [ ] This PR changes the CI/CD test suite
  • [ ] I have tested my suite changes are well-formed (all tests can be discovered)
  • [ ] These changes adjust existing test cases
  • [ ] These changes add new test cases
• [ ] This PR changes prose (such as the documentation, README or other Markdown/RST documents)
  • [ ] I have proofread my changes for grammar and spelling issues
  • [ ] I have tested that any changes regarding Markdown/RST syntax result in a well formed document