Documentation - Add Instructions for integrating into existing Prometheus and Grafana environments

[CarlB-dev]

Currently the installation instructions are explicitly for a self contained environment, but many customers already have either a Prometheus and/or a Grafana environment.

Expected behavior
Provide instructions on installing the necessary changes to the components to allow a custom Prometheus and Grafana deployment to be used with the OTEL_COLLECTOR container.

Additional context
The Grafana Dashboards are in the repository already in JSON format, so we simply need to alter the docs to make the users aware of them and how to import them and set up the datasource for the AST Dashboards.

Are there changes to the config helper python scripts as well when an existing prometheus and grafana system are used?

[mikempw]

We will provide those instructions, but if a customer does this, they will lose the benefits coming in later releases. I’d suggest sending the data to ast Prometheus along with a customers already baked tooling, so they can see the benefits of it in later releases.