Support for dns-persist-01 challenges #263
Description
See the Let's Encrypt announcement for more background. Support in Pebble landed in v2.10.0+.
It would be nice to support this in instant-acme. However, since draft-ietf-acme-dns-persist-00 is very early in the standardization & CA support life cycle and we should probably explicitly declare any supporting code on our side as experimental so it can be adjusted outside of semver expectations.