Changes:
- fix: replace on_attach and custom_attach with autocommand for LspAttach
as recommended by the official documentation.
- fix: enable inlay hints for gopls.
- fix: add a keymap to toggle inlay hints for supported versions of
neovim.
- fix: customise the NormalFloat background colour.
- fix: add LSP configuration for the Lua Language Server.
- refactor: move the lint autocommand to lint.lua
