Subsampling DNS events to reduce logs

Currently, each device generates about 4000 queries per day.
Reduce the number of events by subsampling events based on
how interesting they are:
- if return_code == 0 -> log 1 in 100 events (random sampling)
- if return_code == EAI_NODATA -> log 1 in 10 events (random sampling)
- else -> log 100%
Also allow to use experiment flag to update sub-sampling denom.

Example for dumpsys dnsresolver:
  NetId: 100
    DnsEvent subsampling map: default:1 0:100 7:10

Bug: 119862317
Test: manual test with using setprop to change subsampling map
      atest
Change-Id: Ie0a433a91f629dd32b1d0787a5b45926415faab0