Calculate dashboard stats and save to db

# 💡 Summary #
Create a new table to hold dashboard statistics. Also create a scan that will fill the table ever X minutes.

## Motivation and context ##
This will allow us to query the pre-calculated statistics for the dashboard so we won't time out running the queries
## Implementation notes ##
Create new dashboard-stats table in the Crossfeed db
Create scan to query the stats and save them to the table every X minutes.
Create endpoint to pull stats to be used by the frontend
## Acceptance criteria ##

How do we know when this work is done?

- [ ] Frontend dashboard is populated from the new dashboard stats table

No files, tests, scan entry points, or endpoint names are identified in the issue. Start by locating the existing dashboard queries, scan jobs, database migrations, and dashboard API/frontend code; confirm how often the scan should run. Done means the statistics are stored, refreshed on that schedule, served by an endpoint, and used to populate the frontend dashboard.

Written by the indexing model from the issue text.