adapter: add enable_mz_notices feature flag

[aalexandrov]

Gate tracking of optimizer notices in the catalog behind a feature flag.

Design doc

Motivation

• This PR adds a feature that has not yet been specified.

The bot in #23360 suggested to gate this behind a feature flag.

Tips for reviewer

• The hard-coded default is true, otherwise we might not be able to pick all updates on the first deployment because the LD flag is synchronized after the bootstrap call.
• Currently only gates the packing of retractions / insertions.
• We should also add a change to misc/python/materialize/mzcompose/__init__.py, but as we saw earlier this week this doesn't quite work at the moment because regression tests picking up the last stable version and emit a warn if the DEFAULT_SYSTEM_PARAMETERS contain a parameter that is not supported by that version.

Checklist

• This PR has adequate test coverage / QA involvement has been duly considered.
• 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).
• This PR includes the following user-facing behavior changes: