Consume events from page-change.

@dcausse @otto @tchin @lbowmaker

Closes: T311084

Refactor the Mediawiki Stream Enrichment job to consume events from the consolidated page-change stream. The following change have been introduced:

1. Replace schemas defined by cases classes with a Row object.
2. Integrates WMF boilerplate for stream configuration.
3. Simplifies the Async enrichment function logic.

An entry point to review code could be enrichment/src/test/scala/EnrichmentSuite.scala.

Dependencies on pending work

1. events should be produced in the page-change stream
2. wikimedia-event-utilities 1.2 should be released with https://gerrit.wikimedia.org/r/c/wikimedia-event-utilities/+/810387 merged
3. Page change schema has been finalised
4. Enriched page change schema has been finalized.

TODO:

1. Implement a checkpointing and offset management strategy,