chore: update to 5.3.2 tag

Related to #17 (closed) and #16 (closed)

/cc @twalker - from what I can tell there is no new tag on the github repo for prometheus-exporter, but there is a 5.3.2 image on dockerhub. This MR just updates the tag (+ fixes the base image reference) to keep in sync with the dockerhub versioning. If anything else is needed let me know!