[Docs] Prometheus references, either remove or link out to Prometheus docs

Is your feature request related to a problem? Please describe.

Loki is "Like Prometheus, but for logs!"

This assumes that users are already familiar with Prometheus. The project has grown in popularity to the point where we are attracting users who are NOT familiar with Prometheus.

Describe the solution you'd like

Search the documentation for Prometheus references and either:

• Remove the reference and describe how Loki works.
• OR
• Link out to the relevant Prometheus documentation.

Describe alternatives you've considered A clear and concise description of any alternative solutions or features you've considered.

Additional context Prometheus references are confusing and frustrating to new Loki users, since our current documentation make it look like you need to learn Prometheus before you can use Loki.

### Tasks
- [ ] [Storage Docs](https://grafana.com/docs/loki/next/storage/)  "Unlike other logging systems, Grafana Loki is built around the idea of only indexing metadata about your logs: labels (just like Prometheus labels)"  Link to https://prometheus.io/docs/practices/naming/#labels  ?