Scrape metrics from Redis PostgreSQL

[KenPet11]

Relevant to answer the question: what metrics can we scrape?

[brusMX]

1. For PostgreSQL - https://docs.microsoft.com/en-us/azure/postgresql/concepts-monitoring#list-of-metrics
2. For Redis - https://docs.microsoft.com/en-us/azure/azure-cache-for-redis/cache-how-to-monitor#available-metrics-and-reporting-intervals

Now, that doesn't mean that they will all be exposed or that the naming is consistent between the dashboard and the metrics API, we need to verify that. @cnadolny is testing some for PotsgreSQL

[cnadolny]

Verified that Promitor is able to grab the metrics listed here: https://docs.microsoft.com/en-us/azure/postgresql/concepts-monitoring#list-of-metrics

[cnadolny]

Verified that Redis is also able to grab the metrics listed here: https://docs.microsoft.com/en-us/azure/azure-monitor/platform/metrics-supported#microsoftcacheredis