Merge pull request #17108 from rgacogne/ddist-max-oustanding-queries-per-backend

dnsdist: Implement per backend max outstanding queries

diff --cc pdns/dnsdistdist/dnsdist-configuration-yaml.cc
Simple merge

diff --cc pdns/dnsdistdist/dnsdist-lua-bindings.cc
Simple merge

diff --cc pdns/dnsdistdist/dnsdist-settings-definitions.yml
Simple merge

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

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