index history endpoint #161
Description
With the introduction of incremental indexing in #147 there is now an index_history.parquet file. This file records the times of indexer runs and basic information about the outcomes of each indexer run.
It should be considered similar to the errors.parquet file as it reports information that is interesting to an administrator and is not sensitive.
A new endpoint should be added to report the content of index_history.parquet via the API to make it simpler to monitor indexer progress over time.