Feat: Add Color Configuration (#82)

This MR adds the ability to customize colors for the discussion tree

lua/gitlab/state.lua

@@ -59,6 +59,13 @@ M.settings = {
   },
   go_server_running = false,
   is_gitlab_project = false,
+  colors = {
+    discussion_tree = {
+      username = "Keyword",
+      date = "Comment",
+      chevron = "Comment",
+    },
+  },
 }
 
 -- Merges user settings into the default settings, overriding them