Merge pull request #13537 from rgacogne/ddist-packetcache-max-size

dnsdist: Make the max size of entries in the packet cache configurable

diff --cc pdns/dnsdist.cc
Simple merge

diff --cc pdns/dnsdist.hh
Simple merge

diff --cc pdns/dnsdistdist/docs/reference/config.rst
Simple merge

diff --cc regression-tests.dnsdist/test_Caching.py
Simple merge