Add option to use more subtle highlight for LspReference{Read/Write/Text}

[DefinitelyNotSimon13]

The way the LspReference{Read/Write/Text} highlights currently look are in my opinion to imposing and distracting:

Furthermore - at least for catppuccin - this is also not how the originial catppuccin theme looks.

When setting ui.base64.subtle_hover = true the used colors are changed:

local nvconfig = require "nvconfig"
local subtle_hover = nvconfig.ui.subtle_hover or nvconfig.base46.subtle_hover

local lspReferenceText, lspReferenceRead, lspReferenceWrite

if subtle_hover then
  lspReferenceText = { bg = colors.grey }
  lspReferenceRead = { bg = colors.grey }
  lspReferenceWrite = { bg = colors.grey }
else
  lspReferenceText = { fg = colors.darker_black, bg = colors.white }
  lspReferenceRead = { fg = colors.darker_black, bg = colors.white }
  lspReferenceWrite = { fg = colors.darker_black, bg = colors.white }
end

return {
  -- LSP References
  LspReferenceText = lspReferenceText,
  LspReferenceRead = lspReferenceRead,
  LspReferenceWrite = lspReferenceWrite,
  [...]
}

This results in the hovered/related elements looking like this:

I've also created a draft pull request to add this option to nvconfig.lua file.

[siduck]

why subtle_hover?

I like this style, keep it default. Users not liking it can just use hl_override

[siduck]

just make them into -> bg=one_b3

[DefinitelyNotSimon13]

why subtle_hover?

I like this style, keep it default. Users not liking it can just use hl_override

Wasn't sure if the original setting was as it is on purpose - changed it to always be one_b3