Zoekt reallocate log node name & return early when no work

What does this MR do and why?

Updates to zoekt reallocation task in Search::Zoekt::SchedulingService

• Only log in reallocation when
  • nodes over watermark are detected
  • when namespaces are being moved
• add node name to logs when namespaces are removed
• add total repository size moved to logging (to help us tie this work to volume capacity changes)
• move zoekt node info under meta.zoekt in logs
• small code refactor to make rubocop happy
• specs

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

N/A

How to set up and validate locally

logging changes