## What is this PR for?
Worksheet hovering is a useful feature provided by `metals` to see not
just the end result, but also the entire output of a function call, as
can be seen here for example:
https://youtu.be/Jv9B1crzpWM?t=16m20s
Having a default key assigned not only makes it more convenient, but
also increases discoverability.
(I was also contemplating `<leader>mK` as the mapping to be in line with
`K` for regular hover, but I wasn't convinced that the consistency is
worth the extra keypress.)
## Checklist
- [x] I've read the
[CONTRIBUTING](https://github.com/LazyVim/LazyVim/blob/main/CONTRIBUTING.md)
guidelines.
