Description of the problem:
The install on existing RHDH instructions need some updates. Since several customers are deploying the orchestrator using the GA RHDH Helm chart + the orchestrator operator, our instructions should also reflect this installation method as well.

1. Information about the postgres DB should be in the Prerequisites section. Not all users access these instructions via the doc website first
and they may miss that the postgres db needs to be set up (or that an existing DB needs to be configured to be used). 

2. In the Install the Orchestrator Operator section, a note should be added to point 2 - create orchestrator resource, that the default values for the postgres section may not match what the user has and should reflect the user's configuration.

3. In the example orchestrator resource given, the field "name" and "namespace" should be added, as the operator uses those fields to create the networkpolicies. Otherwise the user will think that they are optional if installOperator is set to false.

4. If Helm was used to deploy RHDH, not the RHDH operator, the name of the secret used to point to the NPM registry should be  <Release name>-dynamic-plugins-npmrc instead of dynamic-plugins-npmrc. This should be specified in the Prerequisites section and the [Edit RHDH configuration|https://github.com/rhdhorchestrator/orchestrator-go-operator/blob/main/docs/release-1.5/existing-rhdh.md#edit-rhdh-configuration section.

Expected results: This should be updated for 1.5 and 1.6.