Fix command in telemetry installation

There are missing/incorrect commands in the [Install Telemetry Backend](https://open-match.dev/site/docs/guides/telemetry/#install-telemetry-backend) helm steps in the documentation
`helm install my-release --namespace open-match open-match/open-match \
--set open-match-override.enabled=true \ # Install the default override configmap
--set open-match-telemetry.enabled=true \ # Enable telemetry logic in Open Match core
--set global.telemetry.jaeger.enabled`

should be set to
`--set global.telemetry.jaeger.enabled`

And there are missing steps to install Prometheus and Grafana in the helm section