modified Dockerfile/prebuild.sh script to reflect most recent GPG/sha, Whitelist Precedures

• modified Dockerfile/prebuild.sh script to reflect most recent GPG/sha requirements; added an Examples file to provide more examples for Dockerfiles or scripts; updated documentation regarding other requirements (e.g. License, Healthcheck)

• later modification: added instructions to Whitelist Procedures and added examples, including ubi7 justifications documents; definitely needs review for accuracy.