Refactor: Rename lualine_conifg.lua -> lualine/config.lua

This is loaded by lualine require so the peroformence will not be effected.

lua/lualine.lua

@@ -7,7 +7,7 @@ local modules = lualine_require.lazy_require{
   utils_section = 'lualine.utils.section',
   utils = 'lualine.utils.utils',
   utils_notices = 'lualine.utils.notices',
-  config_module = 'lualine_config',
+  config_module = 'lualine.config',
 }
 local config           -- Stores cureently applied config
 local new_config = true  -- Stores config that will be applied

lua/tests/spec/config_spec.lua

@@ -1,7 +1,7 @@
 local eq = assert.are.same
 
 describe('config parsing', function()
-  local config_module = require 'lualine_config'
+  local config_module = require 'lualine.config'
 
   describe('options', function()
     describe('icons_enabled', function()