Create an informative issue (See each section, incomplete templates/issues won't be triaged)

Using the current documentation as a model, please complete the issue template. 

Note: Doc team updates the current version and the two previous versions (n-2). For earlier versions, we will address only high-priority, customer-reported issues for releases in support.

Prerequisite: Start with what we have

Always look at the current documentation to describe the change that is needed. Use the source or portal link for Step 4:

 - Use the Customer Portal: https://access.redhat.com/documentation/en-us/red_hat_advanced_cluster_management_for_kubernetes

 - Use the GitHub link to find the staged docs in the repository: https://github.com/stolostron/rhacm-docs 

Describe the changes in the doc and link to your dev story

Provide info for the following steps:

1. - [x] Mandatory Add the required version to the Fix version/s field.

2. - [ ] Mandatory Choose the type of documentation change.

      - [x] New topic in an existing section or new section

A new topic named Customizing URLs in the Customize Observability section. In this new topic we will teach the customers how to customize the Observatorium API and Alertmanger URLs that are used by spoke clusters. 

      - [ ] Update to an existing topic

3. - [ ] Mandatory for GA content:
            
       - [x] Add steps and/or other important conceptual information here: 

We are adding the capability of customizing both the URLs of the Observatorium API and Alertmanager that the spokes will use to talk back to the Hub. To enable this, two new configuration options are being added in the advanced section of the MultiClusterObservability Spec:

spec:
  advanced:
    customObservabilityHubURL: <URL here>
    customAlertmanagerHubURL: <URL here>

In addition to this step, Route objects will have to be manually created.

For a custom Observability Hub URL:

Create the route below, note that it's mostly a copy of the Observatorium API Route, but with a different name and host that matches the intermediate's component URL.

apiVersion: route.openshift.io/v1
kind: Route
metadata:
  name: proxy-observatorium-api
  namespace: open-cluster-management-observability
spec:
  host: <INTERMEDIATE_COMPONENT_URL>
  port:
    targetPort: public
  tls:
    insecureEdgeTerminationPolicy: None
    termination: passthrough
  to:
    kind: Service
    name: observability-observatorium-api
    weight: 100
  wildcardPolicy: None

For a custom Alertmanager URL:

Create the route below, note that it's mostly a copy of the Alertmanager Route, but with a different name and host that matches the intermediate's component URL:

apiVersion: route.openshift.io/v1
kind: Route
metadata:
  name: alertmanager-proxy
  namespace: open-cluster-management-observability
spec:
  host: <INTERMEDIATE_COMPONENT_URL>
  path: /api/v2
  port:
    targetPort: oauth-proxy
  tls:
    insecureEdgeTerminationPolicy: Redirect
    termination: reencrypt
  to:
    kind: Service
    name: alertmanager
    weight: 100
  wildcardPolicy: None

Limitations

• Both systems only support intermediate components with TLS passthrough.

• If both custom URLs are provided are pointing to the same intermediate component, separate sub-domains will have to be used. This is required because OpenShift routers do not support two separate Route objects with the same host.

       - [ ] Add Required access level for the user to complete the task here:
       

       - [ ] Add verification at the end of the task, how does the user verify success (a command to run or a result to see?)
     
     
       - [x] Add link to dev story here: https://issues.redhat.com/browse/ACM-10706

4. - [ ] Mandatory for bugs: What is the diff? Clearly define what the problem is, what the change is, and link to the current documentation: