ct: implement CREATE TABLE .. TRANSFORM .. USING as syntactic sugar

[danhhz]

The parser learns to recognize CREATE TABLE .. TRANSFORM .. USING (..)
and de-sugars it into a CREATE CONTINUAL TASK statement. This allows
us to incrementally ship a smaller footprint than the full generality of
the feature. The statement remembers how it was typed in and we can have
separate feature flags, but otherwise planning etc only see this as a
normal CT.

Touches https://github.com/MaterializeInc/database-issues/issues/8427

Motivation

• This PR adds a known-desirable feature.

Tips for reviewer

Syntax very much a strawman that we'll want to hash out with sql-council. Inspired by CREATE TABLE .. FROM SOURCE, for which I think there are good parallels:

• Maybe you want more than one TRANSFORM USING for a source, etc.
• 1:1 relationship between statements and objects (for things like dbt/terraform).
• A one-output CT kinda feels like a read-only table? Super long-term I think we could even allow user writes to this table?

Checklist

• This PR has adequate test coverage / QA involvement has been duly considered. (trigger-ci for additional test/nightly runs)
• This PR has an associated up-to-date design doc, is a design doc (template), or is sufficiently small to not require a design.
• If this PR evolves an existing $T ⇔ Proto$T mapping (possibly in a backwards-incompatible way), then it is tagged with a T-proto label.
• If this PR will require changes to cloud orchestration or tests, there is a companion cloud PR to account for those changes that is tagged with the release-blocker label (example).
• If this PR includes major user-facing behavior changes, I have pinged the relevant PM to schedule a changelog post.