feat: raw json (string or serde_json::Value) instead of structs

added Feature label

@aditeya.vg Progress can be made on this feature once this PR gets accepted and merged: https://github.com/puetzp/prometheus-http-query/pull/11

created branch 14-feat-raw-json-string-or-serde_json-value-instead-of-structs to address this issue

mentioned in merge request !17 (merged)

mentioned in commit 1f9b5519

closed with merge request !17 (merged)