add messages intent

[MaskDuck]

Rationale

I wanna know if my bot has enabled the brand new messages intent without looking into the code.

Summary of changes made

I added the line messages intent, this should be see in the jsk command.

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 (no need to do)
• [ ] 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

[MaskDuck]

It should return this using my jishaku: (sorry i am using light mode lol)

[JDJGInc]

I would legit use this. I don't think there's a specific thing for message intent though

[scarletcafe]

Pretty sure this should be closed by https://github.com/Gorialis/jishaku/commit/85d9844957445a671266007828ba4f12f29ec362, but if some lib is specifically using intents.messages as opposed to intents.message_content let me know and I'll adjust stuff.