Fix a link to the Slash commands page

`/user/project/slash_commands.md` was redirecting to
`/user/project/quick_actions.md` but the correct page is
`/integration/slash_commands.md`

doc/operations/incident_management/index.md

@@ -58,7 +58,7 @@ GitLab creates a unique endpoint which receives a JSON-formatted, customizable p
 Slack slash commands allow you to control GitLab and view GitLab content without leaving Slack.
 
 Learn how to [set up Slack slash commands](../../user/project/integrations/slack_slash_commands.md)
-and how to [use the available slash commands](../../user/project/slash_commands.md).
+and how to [use the available slash commands](../../integration/slash_commands.md).
 
 ## Integrate issues with Zoom