Enable a publishing with a rolling tag

[dmikusa]

Describe the Enhancement

When publishing code updates, there are some scenarios where it is helpful to have a tag that rolls and updates automatically (like container image tags). Ex: v2 always points to the latest v2.x.x. Enable pipeline builder to support this scenario.

Possible Solution

1. Add a pipeline-descriptor property. When enabled, this will trigger the publishing job to run, look at a particular set of tags (probably based on a prefix), find the most recent tag and then update the rolling tag to it.

2. This won't apply to buildpack publishing, just for publishing libraries or publishing binaries.

Motivation

For octo, we often just want it to use the "latest", but that is confusing because we have different major branches. This feature would enable us to say something like go install github.com/paketo-buildpacks/pipeline-builder/octo@v2-latest and every time that CI job runs, it'll fetch the latest branch.