Addition of FlagInputModal (#1606)

## Description:

The UI for selecting flags differs from other existing UIs, so this
change allows it to use .
The actual contents for flag selection will be included in the next PR.

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced
- [x] I have read and accepted the CLA agreement (only required once).

## Please put your Discord username so you can be contacted if a bug or
regression is found:

aotumuri

---------

Co-authored-by: Scott Anderson <662325+scottanderson@users.noreply.github.com>

src/client/index.html

@@ -411,6 +411,7 @@
     <news-modal></news-modal>
     <game-left-sidebar></game-left-sidebar>
     <spawn-ad></spawn-ad>
+    <flag-input-modal></flag-input-modal>
     <fps-display></fps-display>
     <div
       id="language-modal"