Add config setting if the collector registry should be wiped

[ekateiva]

TL;DR;

We can't wipe metrics on each metrics render, if we want to use Counter metric.

Why this change?

I am working to introduce Counter metric type. This metrics works a bit different than Gauge. Counter could be set somewhere in the code and executed multiple times during the period between data sync to Prometheus. Of course, for this we need to use different Storage (not InMemory). But this is a different topic, and right now it can be overwritten in the container. In the future maybe this package could also have a storage setting.
And Counter value always goes up, so we don't need to wipe the storage on each request. Also, I don't see a reason, why we should wipe it for InMemory storage as well, as the Gauge exporters right now works in the same request cycle.

Some packages already have such a setting and is off by default:

• https://github.com/LKaemmerling/laravel-horizon-prometheus-exporter/blob/master/config/config.php#L42

Others don't have such setting, but don't wipe as well:

• https://github.com/arquivei/laravel-prometheus-exporter/blob/master/src/MetricsController.php

Looking forward to hear your opinion on that. Otherwise, we need to override the RenderAction just to remove $this->registry->wipeStorage(); line. So maybe it's better to have in the package under the setting.

[freekmurze]

Thanks!