Update Grafana dashboard

[nscuro]

Description

This PR applies various updates to the example Grafana dashboard.

General

• Most, if not all, widgets now have a description of what they are about
• rate is used instead of increase for metrics of type counter
  • This aligns more with industry standards
• rate is applied to a static interval of 1 minute (1m) instead of the dynamic $__rate_interval

JVM

New widgets for garbage collector activity. Frequent and long GC pause durations can be a good indicator for insufficient memory, or a hint that experimenting with other GC implementations should be done.

In Hyades for example, we changed the default GC from Parallel GC to G1 for the API server, because we were seeing regular pauses of >3 seconds (DependencyTrack/hyades-apiserver#150) under high load.

Database

New widgets for metrics related to the database connection pools:

• Average time taken for threads to acquire a connection from the pool
• Average time taken to create a new connection for the pool
• Average time connections are used before being returned to the pool

Also included is a widget that shows the current number of entries in the caches maintained by DataNucleus.

Events and notifications

Units of widgets have been adjusted to make it more clear what exactly is shown. Using ops/s makes it a lot easier to understand what the graphs mean. Widgets that display absolute metric values (e.g. number of events queued) are now using bars instead of lines.

Functional

Metrics for various "functional" areas of DT are now displayed in a new Functional row.

Addressed Issue

Additional Details

Checklist

• I have read and understand the contributing guidelines
• This PR fixes a defect, and I have provided tests to verify that the fix is effective
• This PR implements an enhancement, and I have provided tests to verify that it works as intended
• This PR introduces changes to the database model, and I have added corresponding update logic
• This PR introduces new or alters existing behavior, and I have updated the documentation accordingly