feature: Windmill scripts can produce their own custom metrics

[gbouv]

The idea is for any script in Windmill to be able to produce its own metric, which would be collected by a metrics collector to be consumed.

The way we could achieve this would be to re-use Windmill's prometheus instance. Rather than prometheus pulling metrics from scripts, the script would need to push their metrics directly to prometheus, and then consuming the metrics would be done outside of windmill. For the V++ we can think of displaying charts in windmill, but for the V0 we can publish a grafana dashboard

We need to add endpoints to the different SDK for pushing metrics.