feat: Return API and scanner version in the metrics output.

[demeringo]

Two new labels are added to all the metrics: cloud_scanner_version and boaviztapi_version.

Per example:

# HELP boavizta_gwp_use_kgco2eq Global Warming Potential of use.
# TYPE boavizta_gwp_use_kgco2eq gauge
boavizta_gwp_use_kgco2eq{awsregion="eu-west-3",country="FRA",cloud_scanner_version="4.5.6",boaviztapi_version="v1.2.3"} 0.6

[jnioche]

I was picturing more something like

cloud_scanner_version{awsregion="eu-west-3",country="FRA"} "4.5.6"
boaviztapi_version{awsregion="eu-west-3",country="FRA"} "v1.2.3"

assuming of course that the values can be strings. Attaching this info to every single metric generated is useful only if you want to filter based on them. I suppose if you had several instances of CS storing into Prometheus at the same time then that could be relevant. Is that the idea? You could then compare the results for different versions of the API for instance.

[demeringo]

I fully agree on the principle but I think that OpenMetrics / Prometheus metrics format only support numerical values (not string).
I believe that the only way to have strings is to use the labels.

Yes the general idea behind this PR is to provide info to end user in the context of where we collects data during a long time span. In this case we may collect metrics that span several versions of API and as we have seen the values returned for the same resource may evolved with new API version. This can help identify the reason for a change in value.

[jnioche]

I think you are right about the values being numerical only
https://stackoverflow.com/questions/65850083/prometheus-java-client-export-string-based-metrics

Let's go for what you suggested