[NTPFooter] Adding policies to control visibility of footer components

The CL adds a policy to control the visibility of the NTP footer
management notice and theme attribution.

The management notice policy is not per profile since it is shown for
all profiles when the browser is managed. Theme attribution is per
profile as the theme applies to the profile the extension is installed
in.

The policies will be used in follow up CLs.

Bug: 411428900, 409620845
Change-Id: I1bd79fbc4cac6b58867ca47bf34dcac142d89e91
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6479319
Reviewed-by: Igor Ruvinov <igorruvinov@chromium.org>
Reviewed-by: David Roger <droger@chromium.org>
Reviewed-by: Yann Dago <ydago@chromium.org>
Commit-Queue: Salma Elmahallawy <esalma@google.com>
Cr-Commit-Position: refs/heads/main@{#1452671}