SQL Server basic support to handle failover in HA

[martykulma]

Add config variable sql_server_source_validate_restore_history to control SQL server restore history validation behavior.

The default behavior of emitting a definite error remains the same. If validation is disabled, detecting a restore history change will only elicit a warning in the logs.

This also adds 2 checks to dataflow startup to ensure CDC is enabled and the agent is running. CDC requires extra steps after an AOAG failover, without validation, MZ might appear to never make progress because CDC is not actively running.

Motivation

Adds feature https://linear.app/materializeinc/issue/SS-28

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.

[DAlperin]

LGTM, I trust big tech!

[martykulma]

TFTR!