Prerequisite: Start with what we have

Currently we have in the [Docs](https://access.redhat.com/documentation/en-us/red_hat_advanced_cluster_management_for_kubernetes/2.5/html-single/add-ons/index#submariner-globalnet) misleading instructions how to create Broker via manifest:

1.

Replace <broker-namespace> with the name of your broker namespace.

But how can the user know the correct broker namespace ?

2. There's a missing important note - not to change the Broker resource name (just like we have for SubmarinerConfig). 

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

We should instruct to:

1. Get "broker-namespace" by running:

oc get ManagedClusterSet <cluster-set-name> -o jsonpath="{.metadata.annotations['cluster\.open-cluster-management\.io/submariner-broker-ns']}"

2. Add:

Note: The name of the Broker must be submariner-broker, as shown in the example. 
      

1. - [ ] {}Mandatory{} Choose the documentation release (Published releases are refreshed ~weekly after publication). 
     
      - [ X] ACM 2.4
      - [ X] ACM 2.5
      - [ X] ACM 2.6 
      - [ ] MCE 2.0.1
      - [ X] ACM 2.7  (repo opens after the first few release sprints)
      - [ ] MCE 2.0.2 (repo opens after the first few release sprints)
   

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

      - [X ] New topic in an existing section or new section
      - [ ] Update to an existing topic

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

4. - [ ] {}Mandatory for GA content:{}
            
       - [ ] Add steps and/or other important conceptual information here: 
       
            
       - [ ] 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?)
     
     
       - [ ] Add link to dev story here:

   - {}Errata release note{} version, this is NOT for regular refreshes: 
      (published with Errata release)
  
      - [ ] ACM 2.4.x
      - [ ] ACM 2.5.x
      - [ ] ACM 2.6.x

5. {}Optional:{} Get back to issue templates to create more issues for the doc team: https://github.com/open-cluster-management/backlog/issues/new/choose