main.star: add linux-arm64 performance builders

This adds new builders that target the new c4a instances in our fleet
for performance testing.

For golang/go#70231.

Change-Id: I924859344f72cfa331bce296f1d646bccb3589e7
Reviewed-on: https://go-review.googlesource.com/c/build/+/625976
Reviewed-by: Dmitri Shuralyov <[email protected]>
Auto-Submit: Michael Knyszek <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: mknyszek