Load component and index templates as throttled background jobs (max 10
concurrent) instead of sequential curl PUTs, matching the bounded-concurrency
+ flock-serialized-output pattern used by the fleet/ILM load scripts. Keeps a
wait barrier between the component phase and the index phase so index
templates never load before their referenced component templates. Failures are
tracked via per-job marker files since counter increments can't escape
background subshells.
Josh Patterson
43f72c1f9f