fix: update-check.sh should query GH Releases (#3666)

* fix: Source `VERSION` from image ENV

Now CI builds triggered from tagged releases will always have the correct version. No need for manually updating a separate file.

* fix: Query latest GH release tag

Compare to the remote GH release tag published, rather than contents of a `VERSION` file.

`VERSION` file remains in source for now as prior releases still rely on it for an update notification.

* chore: Switch from `yq` to `jaq`

- Can more easily express a string subslice.
- Lighter weight: 9.3M vs 1.7M.
- Drawback, no YAML input/output support.

If `yq` is preferred, the `v` prefix could be removed via BASH easily enough.

* chore: Add entry to `CHANGELOG.md`

* ci: `VERSION` has no relevance to `:edge`

* docs: Update build guide + simplify `make build`

---------

Co-authored-by: Georg Lauterbach <44545919+georglauterbach@users.noreply.github.com>

Dockerfile

@@ -295,8 +295,8 @@ COPY target/scripts/startup/setup.d /usr/local/bin/setup.d
 #
 
 FROM stage-main AS stage-final
+ARG DMS_RELEASE=edge
 ARG VCS_REVISION=unknown
-ARG VCS_VERSION=edge
 
 WORKDIR /
 EXPOSE 25 587 143 465 993 110 995 4190
@@ -327,4 +327,5 @@ LABEL org.opencontainers.image.source="https://github.com/docker-mailserver/dock
 # ARG invalidates cache when it is used by a layer (implicitly affects RUN)
 # Thus to maximize cache, keep these lines last:
 LABEL org.opencontainers.image.revision=${VCS_REVISION}
-LABEL org.opencontainers.image.version=${VCS_VERSION}
+LABEL org.opencontainers.image.version=${DMS_RELEASE}
+ENV DMS_RELEASE=${DMS_RELEASE}