Silently fail to index when ES is unavailable

[zebdelk]

Summary

As a	Dev / Data Manager
I want to be able to	known when something fails to index because ES is down
So that I can	retrigger it (or better yet, see it automatically reindex when the system is up)

To recreate (suggestion, but might need easier steps, if we can come up with any):

• delete all ES indices (or just restart skaffold stack)
• select a dataset to load you know well
• load enough data for it to create the indices
• manually check indexer offsets (optional)
• turn ES to read-only mode (TODO also see if behavior is same or different by just shutting ES down)
• load familiar dataset
• confirm that indexer log has errors writing to ES
• turn ES to write mode again
• confirm that offset has moved to end
• confirm data has not been indexed

One suggested solution is to see if using KafkaConnect (#1241) will handle this for us?