[NTP Customization] Add a menu entry to open the "NTP customization" bottom sheet

This CL adds "Customize new tab page" entry to the main menu and create the coordinator class for the bottom sheet. After this CL, the bottom sheet can be opened directly from the main menu.

The new UI of the main menu is shown in the following screenshot: https://docs.google.com/document/d/1bMRVyyqOd0-cAmyTbL9IhKNU9uSvDdpdCngSzSXIHnk/edit?tab=t.0#bookmark=kix.iy1lun86ua27

The overall user interaction starting from the main menu is demonstrated in the following video:https://drive.google.com/file/d/1TpV22BQutllYwX_hfjq4q0N6ggyczbcl/view?usp=sharing&resourcekey=0-Y3on1-MrAklvUuX-1PyIoQ

Low-Coverage-Reason: OTHER
Bug: 376240434
Change-Id: Ieaf7f36dc26875fe0c5d8c9a95660e5f502af363
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6216681
Reviewed-by: Xi Han <hanxi@chromium.org>
Reviewed-by: Calder Kitagawa <ckitagawa@chromium.org>
Commit-Queue: Yanling Hu <yanlinghu@google.com>
Reviewed-by: Xinyi Ji <xinyiji@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1417599}