Merge pull request #7504 from rgacogne/rec-channel-cleanup

Add rec statistics about ECS response sizes, API endpoint to get a specific stat

diff --cc docs/http-api/swagger/authoritative-api-swagger.yaml
Simple merge

diff --cc pdns/pdns_recursor.cc
Simple merge

diff --cc pdns/recursordist/docs/metrics.rst
Simple merge

diff --cc pdns/recursordist/docs/settings.rst
Simple merge