It appears that to customize the base job template for a work pool in Prefect, you are allowed to make advanced customizations and set specific job variables which could include labels for pods. Unfortunately, the provided excerpts from the Prefect documentation do not contain explicit instructions on how to add a label to all pods.
For specifics on how to customize your work pool template with labels in Prefect, I would recommend that you review the documentation on work pools where you can find advanced customization options, especially on the 'Advanced' tab when creating or editing a work pool. This information should allow you to define the desired labels for your pods.
Here is a link to the documentation related to work pools for further reading:
Prefect Work Pools
If you require more detailed assistance, you might consider checking out existing GitHub issues or discussions for similar queries or consider opening a new issue if necessary.