Automation/configuration in retool for scaling up mz_introspection cluster for specific customers

[jubrad]

Currently mz_introspection, mz_system, and mz_probe clusters need to be resized manually via an ALTER CLUSTER command. While this works it would improve the workflow quite a bit by managing these sizes via an LD flag.

Additionally, for mz_probe, the current size is mz_probe which can't be adjusted outside of a rollout, and can't be configured per customer, in order to resize mz_probe you need to adjust the size to a previously registered cc size, or we need to globally update mz_probe during a rollout for all customers. Making this cluster size configurable via LD would make resizing probe 1000% easier.

Spin off from ##25517