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.

.busted

@@ -0,0 +1,13 @@
+return {
+  _all = {
+    pattern = "_spec",
+    lpath = "lua/?.lua;lua/?/init.lua",
+    ROOT = {"lua/gitlab"},
+  },
+  default = {
+    verbose = true
+  },
+  tests = {
+    verbose = true,
+  },
+}