Distributor validation middleware does not return early when context is canceled

[seizethedave]

Describe the bug

A recent trace showing 8+s spent in distributor's middleware:

In this request, a (large) OTLP translation completed before the 5 second deadline, but request validation kept on trucking 8 seconds into the request.

Expected behavior

Distributor validation middleware should return reasonably soon after the context is canceled.

Environment

• Infrastructure: K8s

Additional Context