[PHP-FPM] Make dashboard useful for multi node setups

After adding the PHP-FPM integration to our nodes (related: #11760) we checked out the default dashboard and found it's not useful for a multi node setup since it seems to rely on the latest document.

So for example "Accepted connection" will show the value for a different host on each refresh with the default of the `Host Name` selection set to `any` with no useful selection available (`Host Name` = `http://localhost:8080`?).

(For our use case, the "Accepted connections" would jump around between 5mio and 6mio (since it's a summary/counter), also making the graph next to it kinda strange. I'm not sure what it's intended to visualize.)

So what we had to do, was to "duplicate" the Dashboard and change the backing field for the selection (from `service.address` to `agent.name`, since there is no (real)`host.name` field available in these documents), immediately losing the benefit of a managed dashboard just by trying to make it work.

What we would love to see:

* make the dashboard usable for multi node setups
* allow for an overview of the general (FPM) "state" over *all* nodes *without* the need to have to select one node in the dropdown, memorize/screenshot the shown values/graphs and then select another node and compare it

Thank you!