Add device config flag to ignore clipboard source package

Allows testing of remote copy clipboard UI without going through
Nearby. Effectively guarded by the CLIPBOARD_REMOTE_BEHAVIOR flag as
the isRemoteCopy method will only be run if that flag is enabled.

Bug: 246808749
Test: manual, using Clipboard Spammer app
Change-Id: I2a90709e61489d6ff5ae418b21d928c628320721