Add sandbox property to the javadoc rule.

The sandbox property indicates whether metalava should only read
inputs explicitly specified on the command line. This CL adds the
property and sets the appropriate configuration for RBE depending
on whether the sandbox is set or not.

Test: built aosp_crosshatch-userdebug with/without RBE_METALAVA.
Change-Id: I7256d29f18e0af18dbe65d1c7dbbf62fd3d65f4c