add single user server spawn delay and user-facing message #825
  Add this suggestion to a batch that can be applied as a single commit.
  This suggestion is invalid because no changes were made to the code.
  Suggestions cannot be applied while the pull request is closed.
  Suggestions cannot be applied while viewing a subset of changes.
  Only one suggestion per line can be applied in a batch.
  Add this suggestion to a batch that can be applied as a single commit.
  Applying suggestions on deleted lines is not supported.
  You must change the existing code in this line in order to create a valid suggestion.
  Outdated suggestions cannot be applied.
  This suggestion has been applied or marked resolved.
  Suggestions cannot be applied from pending reviews.
  Suggestions cannot be applied on multi-line comments.
  Suggestions cannot be applied while the pull request is queued to merge.
  Suggestion cannot be applied right now. Please check back later.
  
    
  
    
this PR allows admins to add a delay to single-user server spawns (useful for testing), and adds a configurable message to present to users after an amount of time has passed, imploring patience.
adding a delay was useful in debugging some grafana metrics (berkeley-dsep-infra/datahub#4237, berkeley-dsep-infra/datahub#4241).
the 'patience message' was added as users would believe that hubs were down/not working/etc when it took longer than a couple of minutes to launch their notebooks, particularly when a new GCP node was spinning up during peak usage times (berkeley-dsep-infra/datahub#3845, berkeley-dsep-infra/datahub#3963).
this has been incredibly useful for us at UC Berkeley and has saved both us and our users many hours of unnecessary support and debugging requests due to slow launches.
ref: #651