support list all users alertmanager configs and rule groups

[lzh-lab]

Is your feature request related to a problem? Please describe.

Aa a administrator, I want to see all alertmangaer configs and rule groups

Describe the solution you'd like

Add a api or web to list all configs and rules

[stale]

This issue has been automatically marked as stale because it has not had any activity in the past 60 days. It will be closed in 15 days if no further activity occurs. Thank you for your contributions.

[pracucci]

Still valid and we actually have a PR open (to be reviewed).