Merge pull request #16487 from pieterlexis/chore-rm-boost-optional

chore: Switch trivial usage of boost::optional to std::optional

diff --cc pdns/recursordist/rec-main.cc
Simple merge

diff --cc pdns/recursordist/rpzloader.cc
Simple merge

diff --cc pdns/recursordist/syncres.cc
Simple merge

diff --cc pdns/recursordist/syncres.hh
Simple merge

diff --cc pdns/recursordist/test-rpzloader_cc.cc
Simple merge