feat: Add config opt 'ignore_install'

This option allows the caller to define a list of conform formatters
that should be ignored during the install process. This might be useful
if the caller already have this tools installed and prefer not to have
them downloaded again by mason.

lua/mason-conform/auto_install.lua

@@ -2,6 +2,7 @@ local registry = require("mason-registry")
 local mapping = require("mason-conform.mapping")
 
 local function auto_install()
+    local config = require("mason-conform").config
     local formatters_by_ft = require("conform").formatters_by_ft;
 
     local formatters_to_install = {}
@@ -19,6 +20,13 @@ local function auto_install()
         end
     end
 
+    -- Filter out formatters that the user wants to ignore
+    for _, formatter_to_ignore in pairs(config.ignore_install) do
+        formatters_to_install[formatter_to_ignore] = nil
+    end
+
+    print(vim.inspect(formatters_to_install))
+
     for conformFormatter, _ in pairs(formatters_to_install) do
         local package = mapping.conform_to_package[conformFormatter]
         if package ~= nil then