Address duplication of docs regarding utility buildpacks

[fg-j]

What happened?

Currently, many Paketo language family buildpacks' order groups include utility buildpacks like the CA Certificates buildpack and the Procfile buildpack. This means that language families share some user-facing configurability.

Right now, we document this configurability to different degrees in three places: the "Configuring Paketo Buildpacks" section of the site, within each language family buildpack's docs pages, and in the READMEs on the utility buildpacks' repos. We've got duplicated docs and a smattering of different info in different places.

It'd be great to somehow consolidate this information or have a single source of truth for it that can be propagated to multiple locations. This will reduce the likelihood that different copies of similar docs diverge and fall out of date.

Checklist

• I have included log output.
• The log output includes an error message.
• I have included steps for reproduction.

[kvedurmu]

This makes sense to me. I would like to see us linking to the Configuring Paketo Buildpacks page as much as possible for all of these utility buildpacks. Once this PR gets merged, we should have documentation for all Utility Buildpacks that we can link to: Procfiles, CA Cert, Image Labels, Environment Variables.