feat: support regex automod

[onerandomusername]

Summary

implements discord/discord-api-docs#5504

This has been tested in a private server.

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 task lint
  • I have type-checked the code by running task 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, ...)

[shiftinv]

The documentation for AutoModActionExecution.matched_keyword should mention regular expressions as well, looks like that field is being reused:

{
    "t": "AUTO_MODERATION_ACTION_EXECUTION",
    "s": 12,
    "op": 0,
    "d": {
        "user_id": "",
        "rule_trigger_type": 1,
        "rule_id": "984891789930557500",
        "matched_keyword": "literally 1\\s*9\\s*8\\s*4",
        "matched_content": "literally 1 9 8 4",
        "content": "wow this is literally 1 9 8 4 smh",
        ...
    }
}

[onerandomusername]

@shiftinv I added a mention of matched_keyword possibly containing regex in 5805f24