Enhancement: Change metrics check scripts to support PromQL

As suggested in https://github.com/grafana/integration-sample-apps/pull/33#discussion_r1970449518 it would be great to have support for full PromQL queries.

That suggestion recommended Promtool, which unfortunately requires a full Prometheus install to be downloaded, adding dependencies both locally and to CI.

Let's investigate options that we could take here, including potentially a full list of exported queries from the dashboards in the mixins, which could then be URL encoded and submitted via curl (as a low profile solution)

CC @v-zhuravlev