migrate checkin rules editor to vue3

- move constants to a module
- move reading from and writing to non-vue html to django interop module
- switch to composition api and script setup sfc with pug
- use optional chaining operators a lot to simplify code

.editorconfig

@@ -0,0 +1,5 @@
+[*.{js,jsx,ts,tsx,vue}]
+indent_style = tab
+indent_size = 2
+trim_trailing_whitespace = true
+insert_final_newline = true