chore: update project configs to match cp.nvim

- Add .editorconfig
- Add .luarc.json for LSP support
- Rename .stylua.toml to stylua.toml
- Update .gitignore

.editorconfig

@@ -0,0 +1,9 @@
+root = true
+
+[*]
+insert_final_newline = true
+charset = utf-8
+
+[*.lua]
+indent_style = space
+indent_size = 2