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.

• ACM 2.8.0

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

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

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

Prometheus Alertmanager upgrade to v0.25.0

• In ACM 2.8, Observability has upgraded the prometheus-alertmanager version from v0.21.0 to v0.25.0.

Maintain selected filters and/or time range

• In ACM 2.8, Observability has updated all dashboards that contain clickable panel links to preserve the URL time range that is selected at the point in time. (i.e: if a user select the relative time range as the last 5 minutes within a dashboard and click a panel link, the next dashboard will also display the last 5 minutes worth of data.)

Allow multiple selection of nodes

• In ACM 2.8, Observability has updated the "USE Nodes" dashboard to allow users to filter the dashboard data by multiple node instances, instead of being restricted to just one.

Alerting Dashboards

• In ACM 2.8, Observability will provide 3 new dashboards when the service is enabled. The dashboards are the following:
  • Alert Analysis (Overview dashboard of the alerts being generated within the managed cluster fleet.)
  • Clusters by Alert (Alert dashboard where the user can filter by alert name and view real-time data for clusters where the alert was triggered)
  • Alerts by Cluster (Alert dashboard where the user can filter by cluster and view real-time data for alerts that are firing/pending within the cluster environment)

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

• The user will require access to the ACM Observability Grafana and the `open-cluster-management-observability` namespace.

       - [x] Add verification at the end of the task, how does the user verify success (a command to run or a result to see?)

• To view the dashboards, the user can access the ACM Observability Grafana. By clicking the "Browse" tab under the dashboard navigation tab, the user can click on the Alerts folder and view the alerting dashboards. To view the other dashboards, the user can click on the dashboards under the "General" folder.

• To verify the version, the user can access the observability-alertmanager pod and access the container terminal. From the CLI, the user can type in the following command: `alertmanager --version`. to verify that the alertmanager is using v0.25.0.

      - [x] Add a link to the dev story here: https://issues.redhat.com/browse/ACM-1847, https://issues.redhat.com/browse/ACM-5059, https://issues.redhat.com/browse/ACM-5061, https://issues.redhat.com/browse/ACM-4680

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