Create the quick start guide Grafana config to Otel-demo repo

[VineethReddy02]

At the moment in the Promscale quick start guide, we are using pre-packaged Grafana that includes all the required configuration and dashboards. But we aren't maintaining the source of the image in the Promscale repo as it contains too many files that don't make sense or add any value to this repo. So I created a PR to add the Grafana configuration that's being used in the quick start to Otel-demo repository.

To fix this issue, the below tasks have to be done:

1. Change the vineeth97/promscale-demo-grafana to timescale/promscale-demo-grafana
2. Get the PR created against Otel-demo repo merged.