Add Scala 3 support for uPickle and Circe

[luksow]

Seems that simply hseeberger/akka-http-json#757 could be cherry-picked (as noted in hseeberger/akka-http-json#755).

[pjfanning]

I only just saw this - added #2

[pjfanning]

https://oss.sonatype.org/content/repositories/snapshots/com/github/pjfanning/pekko-http-circe_3/1.40.0-RC3_17-0a23ccd2-SNAPSHOT/ is published - likewise upickle equivalent