feat: add `setup()` as an alias to `init()`

[WieeRd]

setup() is a more common/standard name for a general plugin configuration function. And with lazy.nvim, it allows you to just specify the opts table instead of a whole function call.

{
  "onsails/lspkind.nvim",
  config = function()
    require("lspkind").init({ 
      -- stuffs
    })
  end,
},

{
  "onsails/lspkind.nvim",
  opts = {
    -- stuffs
  },
},

It's a minor QoL improvement, but it also only takes a single line. What do you think?