Add support for partial views

[ryannedolan]

Summary

Add support for materializing views with names foo$bar, which output to sink foo. This enables multiple materialized views to write to the same sink.

Details

We introduce the concept of "partial views", which are views materializing part of a larger table. For example, we can have partial views foo$bar, foo$qux, and foo$qiz, all of which are distinct views but which write to the same sink foo. The corresponding pipelines each have distinct names (e.g. foo-bar), enabling them to be individually deleted, updated, etc.

For now, we don't validate that the sink foo's schema matches what the pipeline will try to write. We can introduce a Validator for this purpose later.

Testing

Manually tested creating "partial views" and inspecting the resulting pipeline SQL:

> create materialized view ads."foo$bar" as ...

The resulting pipelines are named correctly:

$ kubectl get pipelines
...
ads-foo-bar         CREATE DATABASE IF NOT EXISTS `ADS` WITH ();...   Deployed.
...