Align DNS resolver configuration for DFP similar to CDS clusters

*Title*: *Align DNS resolver configuration for DFP similar to CDS clusters*

## Description

Today, Dynamic Forward Proxy doesn't inheriting bootstrap DNS resolver configuration when no custom DNS settings are specified, unlike CDS clusters which properly fall back to the bootstrap config in this scenario.

This causes DFP to use c-ares defaults (4 retries, no `udp_max_queries`, etc.) instead of the configured bootstrap settings. The discrepancy leads to DNS timeouts and broken connections in DFP on our end because it couldn't refresh DNS connections when they became unhealthy, while CDS clusters worked correctly with the same bootstrap config.

Could we align DFP's behavior to what we do for CDS?