Add concurrency limit
What does this MR do and why?
We've been seeing surges of indexing requests that in turn cause OOM events for gitlab-zoekt-indexer. This MR adds a new ZOEKT_IDEXER_CONCURRENCY_LIMIT
env variable to reject requests over the limit to prevent this from happening.
How to set up and validate locally
Numbered steps to set up and validate the change are strongly suggested.
Edited by Dmitry Gruzd