make-container-image: Revised workflow

Add magic handling when --mediawiki-versions contains "next". If
"next" exists in the versions list, create virtual "-next" flavours
for each existing entry in MW_FLAVOURS. These single-version
flavours will be built in parallel with the multiversion images (after
all base images are built in serial).

Also, when --force-version is used, update report.json instead of
overwriting it.

Drop --multiversion-debug-image-name/--multiversion-cli-image-name and
add --multiversion-image-basename/--singleversion-image-basename.

Drop --base-images-only.

Depends-On: scap!995 (merged)
Bug: T402508