Missing docs for multiple tooltip callback options

### Documentation Is:

- [X] Missing or needed?
- [ ] Confusing
- [ ] Not sure?

### Please Explain in Detail...

The docs only provide information for certain tooltip callbacks like label. The other tooltip callbacks do not provide documentation, not even signatures for the structure of the callbacks.

The problem is compounded by the fact that the interface has significantly changed over the years; Stack Overflow posts often provide incorrect advice.

### Your Proposal for Changes

Provide the same level of documentation across all tooltip callbacks.

### Example

https://www.chartjs.org/docs/latest/configuration/tooltip.html#tooltip-callbacks