Implementation of Channel methods for core/db

[toastxc]

Please make sure to check the following tasks before opening and submitting a PR

• [x] I understand and have followed the contribution guide
• [ ] I have tested my changes locally and they are working as intended
• [ ] These changes do not have any notable side effects on other Revolt projects

[toastxc]

I believe all of the requests changes have been implemented ^w^

[toastxc]

sorry I don't think I used the change request feature properly, but all the changes should be ok

[toastxc]

There was a conflict, earlier I added Channel as a dependancy for the DB MutexGuard.

[insertish]

Webhooks just got merged, now conflicting, should be fairly quick to fix.