Since background-update pings don't include the regular legacy environment, they won't include relevant per-installation metrics. This ticket tracks adding:

• the installation.first_seen legacy telemetry event data (as Glean scalars, not as a Glean event that can be missed) (see Bug 1811374)
• per-installation attribution data
• possibly: per-installation provenance data (see Bug 1815023)

We might want to cache all of these things in the background update profile for speed and ease of access.