Releases: use flavor to set the tag suffix

[snh]

• read the CONTRIBUTING guidelines
• raised a GitHub issue or discussed it on the projects chat beforehand
• added unit tests
• added integration tests
• updated documentation if needed
• updated CHANGELOG.md

Moves to using the suffix option in flavor from metadata-action to ensure the suffix is applied to all tags. Without this the Alpine image was ending up with the <version> tag instead of the Debian image.

Also removed the type=raw,value=latest and equivalent options from all three images, as the default behavior of latest=auto in flavor should take care of this. The onlatest=true in the suffix option will ensure the Debug and Alpine images will be latest-debug and latest-alpine respectively.

[snh]

Noting that this will still be required even if the Alpine image is removed (#962), as otherwise the Debug image will end up being tagged with the <version> tag instead.

[kradalby]

Looks reasonable, we have removed Alpine, still happy to have these changes.

[snh]

@kradalby Thanks 😄 I've rebased now that the Alpine removal has been merged.

[juanfont]

Fantastic :)