[Bouncer] Add bouncer feature flag.

The bouncer refactor changes some of the existing behavior. To add an
easy way to revert back to the old behavior, we want to enable/disable
the refactor with a feature flag.

Bug: 240299776
Test: None as this does not change any behavior
Change-Id: I1335325599a554d5d98a2a840169191540165672
Merged-In: I1335325599a554d5d98a2a840169191540165672