Add API endpoints for metrics extraction

[jackleland]

This is slightly open ended as it's not yet clear what information we would like to extract, but from conversations with @mjpritchard et al. it seems like group-level storage usage and performance statistics are a starting point.

Storage usage could be gathered from the catalog and performance from the monitor or catalog databases. These would presumably require additional endpoints added to the API which make RPCs to the appropriate mircoservice, or reuse exisiting endpoints with appropriate datetime bounds. I don't think specific date windows can be specified right now but this might be a nice feature for the UI anyhow, so should probably be added at some point.

How we relate this to specific JASMIN information is a separate issue, as group workspaces would be the scope of interest. These are currently retrieved at log in from the projects portal by querying the user_services_url but there may now be a more appropriate endpoint to use for this.

[bnlawrence]

I think we'll need to do it on an individaul level as well (for storage, and storage tiers, and probably tape pools)