dfp: cleanup and cache feature

[alyssawilk]

Commit Message: Additional Description: Risk Level: Testing: Docs Changes: Release Notes: Platform Specific Features: [Optional Runtime guard:] [Optional Fixes #Issue] [Optional Fixes commit #PR or SHA] [Optional Deprecated:] [Optional API Considerations:]

[repokitteh-read-only[bot]]

As a reminder, PRs marked as draft will not be automatically assigned reviewers, or be handled by maintainer-oncall triage.

Please mark your PR as ready when you want it to be reviewed!

:cat:

Caused by: https://github.com/envoyproxy/envoy/pull/34068 was opened by alyssawilk.

see: more, trace.

[repokitteh-read-only[bot]]

CC @envoyproxy/runtime-guard-changes: FYI only for changes made to (source/common/runtime/runtime_features.cc).

:cat:

Caused by: https://github.com/envoyproxy/envoy/pull/34068 was opened by alyssawilk.

see: more, trace.