Support for nvim 0.11 `virtual_lines = true`

[sand4rt]

Problem

I noticed that the indent lines are missing with vim.diagnostic.config({ virtual_lines = true }):

this is a new feature of nvim 0.11: https://gpanders.com/blog/whats-new-in-neovim-0-11/#virtual-lines

Expected behavior

to show the indent lines

[lukas-reineke]

It should be possible to add support for this, kind of like the inlay hints are.

No idea when I would have time to look at this, PRs would be very welcome.