* Allow overriding kafka host for clickhouse via KAFKA_URL_CLICKHOUSE env var
This is needed when using an external clickhouse which doesn't have the
same access to kafka as in-cluster traffic does.
Note that long-term we might need to also provide better auth mechanisms
here as well.
* Rename env variable
* Add a comment to keep topics in sync
* Clean up code relating to table engines
* Add snapshots for table creation queries
* Remove optional import
* Add snapshot tests for CLICKHOUSE_REPLICATION schemas
Note that these are out of sync with cloud in most cases
* Add another warning comment
* Improve naming
* events dead letter queue CH table
* format
* update schemas
* also store raw payload
* better naming
* make table name more clear
* wip better testing
* remove unused imports
* remove kafka test
* prevent non null test from running on CH migrations
* add kafka testing
* minor tests cleanup
* test naive longer sleep
* make test end-to-end
* address review
* update ttl, format
* refactor delay func, address review
