[NTP][Enterprise] Add sign in with mojo connection

* Adds beginning of integration with Microsoft Authentication Library
  by adding popup sign-in.
* Connects the auth iframe to the promo UI within the NTP using Mojo.
* The proxy for the connection has its instance set when
  `ConnectToParentDocument` is called within the parent page handler
  (|NewTabPageHandler|).

Bug: 377379069, 377380012
Change-Id: Ib2b0dfcb52d8247a657013978b034dd075a0f680
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6055264
Reviewed-by: Roman Arora <romanarora@chromium.org>
Reviewed-by: Nasko Oskov <nasko@chromium.org>
Commit-Queue: Riley Tatum <rtatum@google.com>
Reviewed-by: John Lee <johntlee@chromium.org>
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1404530}