[Misc] Add generic extension points to reduce cross-branch conflicts

[shuwenwei]

This PR bundles a set of small, self-contained and behavior-preserving changes that are introduced ahead of time so that long-lived feature branches do not conflict with master. It only adds extension points / placeholders and does not change existing behavior.

• Information schema: add an SPI extension point and provider registry so extra tables/columns can be registered without touching the built-in schema.
• ConfigNode: allow additional persistence/snapshot processors to be injected through ConfigManager.ConfigManagerContext (new protected hooks).
• RPC: reserve a block of status codes for future use.
• Auth: version the user/role profile file format with an extensible extra-segment region; drop the unused Role/User serialize/deserialize.
• Query: log a set of expected status codes at info level, reserve snapshot/procedure/plan type ids, and add the SetColumnProperties execution flow (AST -> task -> executor -> ConfigNode) with its SQL formatter/visitor hooks.

No behavior change for existing statements; the new extension points and reserved identifiers are inert until a feature uses them.