clickhouse query log entries could include more context

We log a bunch of useful stuff when we make queries to clickhouse (like the SQL that we're executing), but those log messages are lacking context about why we're doing it. It'd be nice if we could preserve the information that's in the logger in the OpContext where we're making the query. That way people can correlate specific external requests (by request id) with specific Clickhouse queries.

This is a little tricky in that we use a client logger today that presumably also has useful key-value pairs (like the clickhouse IP we're connected to?) and I don't know if there's a way to merge two loggers' key-value pairs. But in the worst case we could store the key-value pairs from one of these and by hand extend the other logger with those key-value pairs.

(for an example where this would be useful, see #2994)

Start by locating the OpContext used at ClickHouse query sites and inspect how the client logger and existing query log fields are assembled. Compare the useful context described here with example #2994; done means correlating an external request ID with a specific ClickHouse query while retaining relevant client-logger context.