Move page to new location, update crosslinks

Updates the alert-notification page name to something shorter.
Also updates two crosslinks to the page.

doc/operations/incident_management/incidents.md

@@ -53,7 +53,7 @@ With Maintainer or higher [permissions](../../user/permissions.md), you can enab
 1. Check the **Create an incident** checkbox.
 1. To customize the incident, select an
    [issue template](../../user/project/description_templates.md#creating-issue-templates).
-1. To send [an email notification](alert_notifications.md#email-notifications) to users
+1. To send [an email notification](paging.md#email-notifications) to users
    with [Developer permissions](../../user/permissions.md), select
    **Send a separate email notification to Developers**. Email notifications are
    also sent to users with **Maintainer** and **Owner** permissions.

doc/operations/incident_management/index.md

@@ -13,6 +13,6 @@ generated by their application. By surfacing alerts and incidents where the code
 being developed, efficiency and awareness can be increased. Check out the following sections for more information:
 
 - [Integrate your monitoring tools](alert_integrations.md).
-- Receive [notifications](alert_notifications.md) for triggered alerts.
+- Receive [notifications](paging.md) for triggered alerts.
 - Triage [Alerts](alerts.md) and [Incidents](incidents.md).
 - Inform stakeholders with [Status Page](status_page.md).