Credential exposure when running third-party builders in knative/func

knative.dev/func is is a client library and CLI enabling the development and deployment of Kubernetes functions. Developers using a malicious or compromised third-party buildpack could expose their registry credentials or local docker socket to a malicious `lifecycle` container. This issues has been patched in PR #1442, and is part of release 1.8.1. This issue only affects users who are using function buildpacks from third-parties; pinning the builder image to a specific content-hash with a valid `lifecycle` image will also mitigate the attack.