[NTP][Enterprise] Make multiple source versions of the calendar module

* Added some initial code to support 2 calendar modules with different
  sources. The idea here is to have one element class but 2
  descriptors that know the source type they should pass in. This way
  they show in Customize Chrome Side Panel and the NTP separately.
* A <p> was added to show the calendarSource_ temporarily just
  to help show that the calendarSource_ is being set correctly.
* Marked the "Today's Calendar" string as non-translateable since
  there's not a useful screenshot for it at the moment.

Screenshot:
http://screenshot/58oqyq8iG5x6UsM

Bug: 333561268
Change-Id: I26fb45c6c0dfdb129d083d176588a86fc43bb6b3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5445268
Commit-Queue: Riley Tatum <rtatum@google.com>
Reviewed-by: Roman Arora <romanarora@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1288417}