alter_table: Multiple `GlobalId`s for a single table

[ParkMyCar]

Stacked on top of https://github.com/MaterializeInc/materialize/pull/29694, only look at the last commit.

Prototype, not for merging.

This PR prototypes adding GlobalId "aliases" to Tables to facilitate new versions of a table.

Motivation

Tips for reviewer

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.