metrics: add instance filter to all dashboards

[sukunrt]

This provides an instance filter on dashboards like this:

The script I used to update these is at
https://github.com/sukunrt/go-libp2p/blob/add-instance-script/dashboards/script/script.go

[marten-seemann]

Change looks good, and it works fine in the PL Grafana instance.

Any reason to change the file permissions though?

[sukunrt]

oh no. I didn't notice I'd updated them. Changed them back to 644 as before.