Lava callback latency problem

[nuclearcat]

Right now callback is fastapi, which is async. But callback endpoint is slow, as it need to upload artifacts to kernelci storage.
Even i did threads, it seems still slow. We have grafana monitoring that does plain HTTP request to default / endpoint, and it is
reaching 2-4 seconds latency when we have lot of LAVA submissions.
We need to investigate this, and probably rewrite way how callback works fundamentally.
It might be also totally different issue (for example docker-proxy or nginx), because k8s deployment (production) handling this well, but staging (based on docker containers) is slow.