* CH Migration: exit/entry hostnames in sessions_v2

* Leave only exit_page_hostname, we already record hostnames

* Use ClickHouse DDL in favour of ecto so that cluster is included

* Compress with ZSTD(3)

* Expose Hostname filter in the dashboard dropdown

* Add `exit_page_hostname` to ClickHouse `sessions_v2` schema

* Start tracking hostname changes in sessions

* Implement hostname filter suggestions

* Enable filtering by `event:hostname`

* Add tests for filtering by hostnames

* Ensure filter suggestions work for exit pages too

* Allow overriding hostnames with `send_pageview` mix task

* Remove `:window_time_on_page` flag

It seems that we can remove it after all?

* Initialize `experimental_hostname_filter` query parameter

* Rewrite cache store behaviour with regards to session hostnames

* Work around inconsistent session merging

So that `populate_stats` can get closer to actual ingestion

* Improve top stats test

* Make it possible to filter sessions by entry/exit hostnames

* Update pages tests

* Expose `experimental_hostname_filtering` temporarily in the UI

* Untested yet: also apply experimental filtering to sources

* Introduce `hostname_filter` feature flag

* Format

* Test top sources with hostname filter + experimental flag