Feat: Add Basic Lua Test Suite (#115)

This MR adds a Lua test suite to the project, run via busted, and introduces tests for a number of the utility functions. Subsequent work will have to be done to test functions that use the `vim.api` scope and external packages to the plugin.

lua/gitlab/state.lua

@@ -122,7 +122,7 @@ M.merge_settings = function(args)
 end
 
 M.print_settings = function()
-  u.P(M.settings)
+  vim.print(M.settings)
 end
 
 -- First reads environment variables into the settings module,