Add uploaded/downloaded bytes metric to registry dashboards

This MR modifies the container registry Application Detail and Garbage Collection Detail dashboards to show the total amount of uploaded/downloaded bytes in a given timeframe.

Application Detail: https://dashboards.gitlab.net/dashboard/snapshot/nYVS2GJlZ21I7R39U1Nuu39SeSy9yEWN?orgId=1

Garbage Collection Detail: https://dashboards.gitlab.net/dashboard/snapshot/2H78LFyaMNbS4sdbEp1I4Ndh1XDK9LzN?orgId=1

^ Here we filter by migration_path="new" as for online GC we only care about uploads to the new code path (where online GC operates).