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>

Important details:

1. customObservabilityHubURL and customAlertmanagerHubURL only support https URLs and will automatically prepend the https:// scheme if it's not present. http is not supported.
2. customObservabilityHubURL may include the standard path for the Remote Write API (/api/metrics/v1/default/api/v1/receive). If it's not included, ACM Observability will automatically add it at runtime.

Note that any intermediate component responsible to for the custom Observability Hub URL cannot do TLS termination, because this component relies on MTLS authentication. The custom Alertmanager Hub URL supports intermediate components TLS termination through the already existing bring-your-own certificate instructions.

       - [ ] 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: