Asset Service: Team-Level View

### Description

Current "Assets" are locked away at the Instance-level view. This means we have no full tracking on total storage used by a team, nor can a team owner get a clear picture on what files they have stored in FlowFuse, and where.

If we want to provide tiered access to the Asset store at any point, then we will need a centralised view of how much storage is being used, how much is available, and an insight into the actual data being stored too.

Similar to 'Broker", "Performance", etc. this will be available in the "Operations" section of the navigation.

### Which customers would this be available to

None

### Have you provided an initial effort estimate for this issue?

I have provided an initial effort estimate