Support deleting timeseries by name during schema upgrades

This adds support for listing timeseries by name in a schema upgrade
directory, and deleting all records (schema and data) from those
timeseries during an offline ClickHouse database upgrade. The main goal
here is a relatively simple but effective mechanism to clean up
abandoned timeseries, while we figure out how to implement breaking
changes more robustly.

We alreay have examples of these abandonded timeseries in some existing
installations. The existing effort to move timeseries to TOML also
presents an opportunity to make one-time breaking changes for individual
timeseries. Both of these can be supported with this mechanism.

Fixes #5266