Add comments to refactored metric clean up
Add comments to refactored metric clean up

Signed-off-by: Michael Tsang <12c44a905ab68c8326f7d2c4e35a882987901fa1@jetstack.io>

cert-manager/cert-manager,cert-manager/cert-manager,cert-manager/cert-manager,jetstack-experimental/cert-manager,jetstack-experimental/cert-manager,jetstack-experimental/cert-manager,jetstack/cert-manager,jetstack/cert-manager,jetstack/cert-manager