Use fully qualified image names

[hhiroshell]

Addresses the buildpacks/pack#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.

[AidanDelaney]

Does this image need a registry? I think this may meet your criteria of only being used in the local environment

[hhiroshell]

In my understanding, this image means it is pulled from a remote registry to be used as a build environment, so I thought it should be specified with the registry name.

[natalieparellano]

This should be okay, the daemon will happily accept some-image and index.docker.io/some-image interchangeably.

Side note, while docker.io/some-image is correct, all of our code will resolve a registry-less image name to index.docker.io/<image> so I think using the fully qualified domain would be clearer.