Deprecate existing prefix cache match plugin in favor of new datalayer

[rahulgurnani]

As part of #1942 , prepare data hook and scorer is added for prefix cache plugin. Presently these changes are behind a feature gate. As a follow up, the existing prefix cache plugin needs to be deprecated and feature gate needs to be cleaned up.

[rahulgurnani]

/milestone Data Layer Rework

[rahulgurnani]

Targetted for release v.1.3 , #1830

[rahulgurnani]

/assign @rahulgurnani