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>

target/scripts/start-mailserver.sh

@@ -120,7 +120,7 @@ function _register_functions() {
 
   [[ ${SMTP_ONLY}               -ne 1 ]] && _register_start_daemon '_start_daemon_dovecot'
 
-  [[ ${ENABLE_UPDATE_CHECK}     -eq 1 ]] && _register_start_daemon '_start_daemon_update_check'
+  [[ ${ENABLE_UPDATE_CHECK} -eq 1 ]] && [[ ${DMS_RELEASE} != 'edge' ]] && _register_start_daemon '_start_daemon_update_check'
 
   # The order here matters: Since Rspamd is using Redis, Redis should be started before Rspamd.
   [[ ${ENABLE_RSPAMD_REDIS}     -eq 1 ]] && _register_start_daemon '_start_daemon_rspamd_redis'