Add gauge vec for counting snapshots created/removed per volume

[martinsirbe]

No description provided.

[JamieAP]

Wait no. There are way too many VolumeIDs for this to be sensible,

Do not use labels to store dimensions with high cardinality (many different label values), such as user IDs, email addresses, or other unbounded sets of values.

https://prometheus.io/docs/practices/naming/

[jakekeeys]

there should be tags on the volume you can use

[jakekeeys]

[jakekeeys]

would be good to have both of those in the vec