Add tag to sandbox crashes

This tag in ActivityManager is required to get the sandbox crash stack traces, which will be read by GMSCore and sent to clearcut without any user or device identification.

Bug: 221878062
Test: manual, by causing SdkSandbox Test App (go/sdk-sandbox-manual-testing) crash and logging the resulting DropBox header.
Change-Id: I0f3a771f02027170952ec03d1ef9b4a323c67fa0