add pending field to managed cluster replicas

[jubrad]

Motivation

More prep for graceful reconfig.

Reconfiguration replicas that come up will have a suffixed with -pending and will have a pending field in the cluster replica config.
https://github.com/MaterializeInc/database-issues/issues/5976

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).
• This PR includes the following user-facing behavior changes:

[jkosh44]

Did someone on @MaterializeInc/adapter review the design doc for this? If so, they'd probably be a better reviewer than me.

[maddyblue]

I'll review!

[shepherdlybot]

Mitigations

Completing required mitigations increases Resilience Coverage.

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Risk Summary:

The pull request poses a high risk with a score of 79, indicating a significant likelihood of introducing a bug. This assessment is driven by predictors such as the sum of bug reports in the files changed and the delta of executable lines. Notably, there has been a historical trend showing that pull requests with these characteristics are 108% more likely to cause a bug compared to the repository's baseline. Additionally, the repository's predicted bug trend is on the rise, and there is at least one file modified that has a high frequency of recent bug fixes.

Note: The risk score is not based on semantic analysis but on historical predictors of bug occurrence in the repository. The attributes above were deemed the strongest predictors based on that history. Predictors and the score may change as the PR evolves in code, time, and review activity.

Bug Hotspots:
What's This?

File	Percentile
../catalog/state.rs	99

[def-]

Nightly lgtm: https://buildkite.com/materialize/nightly/builds/8211#_
Coverage only shows upgrade tests missing (expected): https://buildkite.com/materialize/coverage/builds/430
I'll add a commit to test persisting the pending field.

[def-]

Ok, I see, this is actually just a new column in mz_cluster_replicas. I'm wondering why test/sqllogictest/autogenerated/mz_catalog.slt's SELECT position, name, type FROM objects WHERE schema = 'mz_catalog' AND object = 'mz_cluster_replicas' ORDER BY position didn't have to be changed? It seem like we should document and check the new fields too.

[jubrad]

@def- this doesn't yet expose the field as a column in mz_cluster_replicas. Really there should be no functional changes from this pr, just a new field being added to the catalog that for now is always false.

Eventually we will expose it, but we'll want to wait for the rest of graceful reconfig functionality before we do that.

[def-]

All test failures are unrelated flakes, fixed in main.