Enrichment module should not depend on flink-scala

Bug: T310680

Flink 1.15 is a scala-free release.

Drop the Flink vendored filnk-scala and replace it with io.findify:flink-scala-api.

I tried bumping scala version to 2.13, but that resulted in

java.lang.UnsupportedClassVersionError: JVMCFRE003 bad major version; class=sttp/client3/Response, offset=6

Sticking to 2.12 for now, because I want to prioritise https://phabricator.wikimedia.org/T310626. We could do scala upgrades as a substask for that phab.

Tagging @otto @dcausse @tchin as (optional) reviewers.