Get step stats

Processing steps of the key's Organization over the window, in the buckets of getPluginCallStats: baseline (cut into segments and made searchable by keyword), enrichment (vectors added) and accepted_to_searchable (from acceptance to searchable by keyword) time the worker's runs. materialized, segmented, retrieval_ready and enriched are the document timeline's steps, each timed from the step that causes it, so they include the time a Record Version waited for the step. An error is a step that is retried or blocked, with its code. Requires observability:read on a key that grants every Corpus.