Fix LB timeout in QueryServer

[vishalkrishnads]

Description

The query server takes quite a while to process incoming requests. But, most load balancers timeout before the computation can be completed.

As a temporary fix, this PR configures the query handler to send a one byte HTTP 202 response after waiting for P_PROXY_TIMEOUT - 5 seconds if the computation hasn't finished. The client can then reach back out with the same query after a while. If the results are ready, the server responds, or it times out again. The result persists in the cache and can be reused for the same query later.

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This PR has:

• been tested to ensure log ingestion and log query works.
• added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• added documentation for new or modified features or behaviors.