Add new telemetry data points

[VineethReddy02]

Below are the telemetry data points that are missing in the product, Adding these data points helps the product team to understand the usage of the product better.

1. Number of active series: Active series the Promscale is ingesting.
2. JSON endpoint ingest: Is the instance leveraging JSON based ingest endpoint for metrics?
3. Restarts of Promscale: To understand on average how many restarts the Promscale deployment goes through, happy to hear out thoughts from engineers on how to better track the Promscale restarts.
4. Timestamp when the telemetry was calculated: Helps to understand when the telemetry was calculated. To know when the telemetry data was calculated.