Reorder documentation related to building container images

[mbhave]

The current section is misplaced under the Kotlin support. We should keep something high-level in a 4.n section and move the details to this section which is currently out-of-date.

[mbhave]

The misplaced section was fixed in #20608. For the rest of the reordering, we'll tackle it as part of #20813 since the layering docs will need to be updated based on the flat format.