From current data at `event.rc1_mediawiki_page_content_change` we notice that both `dt` and `meta.dt` are never `NULL`:
```
spark-sql (default)> SELECT count(1)
> FROM rc1_mediawiki_page_content_change
> WHERE dt IS NULL;
count(1)
0
Time taken: 69.411 seconds, Fetched 1 row(s)
spark-sql (default)> SELECT count(1)
> FROM rc1_mediawiki_page_content_change
> WHERE meta.dt IS NULL;
count(1)
0
Time taken: 27.15 seconds, Fetched 1 row(s)
```
But from the page change schema, we notice that `meta.dt` is [[ https://github.com/wikimedia/schemas-event-primary/blob/dcffdfafe4aaa14dfcb334283dad16fea7a1a808/jsonschema/mediawiki/page/change/1.0.0.yaml#L94-L122 | not marked as required ]].
This seems incorrect, as, if there was no `meta.dt`, the current partitioning strategy of `event.rc1_mediawiki_page_content_change` would fail.
The ask: make `meta.dt` required on all schemas that declare it.