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

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

Release notes for Observability to mention that we are changing the default retention for all downsampling levels to 365 days. 

This represent a reduction for the 1h-resolution retention, which was previously set to indefinite (zero). This will affect all ** customers using ACM Observability that did not set explicit values in the MultiClusterObservability `spec.advanced.retentionConfig`. If customers upgrading from previous versions wants to stay with the "old" default retention configuration (30d for raw data, 180d for 5 minutes, indefinite for 1 hour) they will have to use the following configuration in the MultiClusterObservability resource:

spec:
  advanced:
    retentionConfig:
      retentionResolutionRaw: 30d
      retentionResolution5m: 180d
      retentionResolution1h: 0d

      - [x] Update to an existing topic

We will need an update to the "Customize Observability section" with the details below.

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

The retention for all resolutions on the retentionConfig mentioned at https://github.com/stolostron/rhacm-docs/blob/2.10_stage/observability/customize_observability.adoc?plain=1#L206 and at https://github.com/stolostron/rhacm-docs/blob/a440e5d9a490982dce33590259493a580df94a0f/apis/observability.json.adoc#L388 have changed to 365d (representing 365 days).   
            
       - [ ] 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: RHOBS-987

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