Option to emit arbitrary text beween build steps

[mikepurvis]

Many CI log viewers permit foldable sections to be created by inserting specific text markers in the log. For example, in Github Actions, these look like this:

::group::{title}
::endgroup::

A popular Jenkins plugin lets the marker be arbitrarily configured.

It would be great if there was config option/flag/envvar that caused buildah to print these type of markers. Container build logs can be pretty long and often the "good stuff" is buried under hundreds or thousands of lines of unhelpful package-installation noise. Buildah could help increase usability for those who are building complex containers but have not yet graduated to the point of pushing workflow logs out to external tools for analysis and archival.