buildpacks v1 in sunset

[glasnt]

https://cloud.google.com/docs/buildpacks/support-policy#support_schedule

We are hard coding the buildpacks version in

cloud-run-button/cmd/cloudshell_open/main.go

Line 356 in 1e0ce96

builderImage := "gcr.io/buildpacks/builder:v1"

We should look to updating this to a newer tag (not "latest", probably)