pkgs/tsdb/[grafana-pyroscope-datasource|parca]: Fix use of request headers in responses
In the parca and the grafana-pyroscope-datasource we were wrongly using the request headers instead of the response
header when communication the results to the backend.
This PR fixes this bug.
Was reported by an user via community slack, who faced issues, with a request header of `content-length: 0` being
inserted by a intermediate proxy.
Christian Simon
549511597c