Add a GSI overlay for the framework package

This overlay is used to override the default value of the config_multiuserMaximumUsers resource in the framework package. This is necessary because the default value of this resource is 1, which is too low for CTS (like ProxyMediaRouter2HostSideTest) to add test users.

Bug: 347122747
Change-Id: I351a96c49b698570f67742b176274124c41018c9
Test: TH