Explanation
To start monitoring all pipelines in a project, use the following command inside a channel:
@azure pipelines subscribe [project url]
The project URL can be to any page within your project (except URLs to pipelines).
For example:
@azure pipelines subscribe https://dev.azure.com/myorg/myproject/
Reference:
https://docs.microsoft.com/en-us/azure/devops/pipelines/integrations/microsoft-teams