Use fully qualified image names

[hhiroshell]

Addresses the https://github.com/buildpacks/pack/issues/1218, specifically the modifications to the documentation.

This PR changes the container image names used in the document to fully qualified names. Currently, I'm adopting the following policies:

• Unless there is a specific reason not to, use registry.example.com for the hostname and example for the organization name.
  • Example: registry.example.com/example/my-app
  • One exception: In for-buildpack-authors/concepts/lifecycle-phases.md I used registry.fake as hostname. Because the name is already used in other parts of the page including terminal recordings, and it's too time-consuming to fix.
• In tutorial pages or similar contexts where commands are expected to work, use an implied hostname to avoid breaking functioning commands.
  • Example: use docker.io/ubuntu:jammy instead of ubuntu:jammy
• Do not add a remote registry name to an image that is built and used only within a local environment.

And I fixed some technical errors like typos found when I read through the documents.