New reference panel: avoid 10s+ loading times for 100 references

Created by: mrnugget

It can sometimes take 10s+ or 30s+ to load the reference panel. Seems to be related to how many cross-repo references/implementations there are.

Example trace: https://sourcegraph.grafana.net/explore?orgId=1&left=%7B%22datasource%22:%22grafanacloud[…]ge%22:%7B%22from%22:%22now-1h%22,%22to%22:%22now%22%7D%7D

Multiple options:

1. Make the backend faster
2. Do not load 100 references/implementations on first load, but load, say, 10, and then in the background fetch more in batches of 10