Setup Prometheus and Grafana in the repository docker-compose.yml

[qdm12]

Reasons

1. The first goal is to have locally easy to test/visualize metrics using Prometheus and Grafana, instead of relying solely on deploying to ECS and using Datadog. This will help to finish Instrument the trie with Prometheus metrics #2229 such that an optimal state trie lazy loading mechanism can be determined.
2. Other developers/end users might not have a Datadog subscription, so using Prometheus and Grafana might be better for them.

Subtasks

• The repository docker-compose.yml must contain a working Gossamer node + Prometheus + Grafana
• Prometheus should be pre-configured to scrap metrics from gossamer:9876 via a configuration file
• Grafana should be pre-configured to use Prometheus as source, and to have a (JSON) dashboard for Gossamer, via configuration files
  • Find an existing Substrate Grafana dashboard JSON and modify it
• Document this in the repository

[qdm12]

Done in #2706