Add `average` to curve metrics #5917

Job	Run time
check-code / mypy	3m 21s
check-code / pre-commit	1m 11s
check-md-links / markdown-link-check	4m 27s
check-package / init-store	8s
check-schema / schema	17s
check-package / pkg-build (ubuntu-latest)	30s
check-package / pkg-check (ubuntu-20.04, 3.8)	1m 7s
check-package / pkg-check (ubuntu-20.04, 3.10)	1m 17s
check-package / pkg-check (macos-11, 3.8)	2m 44s
check-package / pkg-check (macos-11, 3.10)	2m 19s
check-package / pkg-check (windows-2022, 3.8)	7m 1s
check-package / pkg-check (windows-2022, 3.10)	5m 8s
check-package / pkg-guardian	1s
	29m 31s

Provide feedback