stx-init-env: require minimal docker BuildKit

An earlier commit [1] introduced a feature (--build-context) that didn't
exist in older versions of docker. Make sure to use BuildKit (ie "docker
buildx") and require a minimal Dockerfile syntax version.

These features became part of docker around mid-2022.

Docker features and version history:
* BuildKit ("docker buildx") first introduced in Docker Engine 18.06.0
  [https://docs.docker.com/engine/release-notes/18.06/#180600-ce].
* --build-context first appeared in BuildKit 0.8.0 / Docker Engine
  20.10.13
  [https://docs.docker.com/build/release-notes/#080]
  [https://docs.docker.com/engine/release-notes/20.10/#201013]
* BuildKit became default on Linux: Docker Engine 23.0.0
  [https://docs.docker.com/engine/release-notes/23.0/#new]
* Named contexts can be used in COPY --from in Dockerfile 1.4
  [https://docs.docker.com/build/buildkit/dockerfile-release-notes/#140]

TESTS
=============

* Minikube (includes docker):
  - v1.37.0 released 2025-09-09

* Docker Engine:
  - 27.5.1 released 2025-01-22
  - 29.0.4 released 2025-11-24

[1] https://review.opendev.org/c/starlingx/tools/+/968507

Signed-off-by: Davlet Panech <davlet.panech@windriver.com>
Change-Id: Ie73b188a185618b8856baf658dc7f85488408066

stx-init-env

@@ -90,6 +90,8 @@ STX_START_OPTS=
 # It doesn't need to track the build target (e.g. bullseye/trixie)
 COREUTILS_DOCKER_IMAGE="debian:bookworm-20240130-slim"
 
+export DOCKER_BUILDKIT=1
+
 info() {
     local tty_on tty_off
     if [[ -t 2 ]] ; then
@@ -1002,7 +1004,7 @@ if [[ -n "${BUILD_DOCKER_IMAGES}" ]] ; then
         info "Starting to build image: $img:$DOCKER_TAG_LOCAL-${builder_os_codename}"
 
         # Build command base
-        cmd="docker build ${docker_build_args[@]} ${extra_build_args[@]}"
+        cmd="docker buildx build ${docker_build_args[@]} ${extra_build_args[@]}"
 
         # Add dedicated build context ONLY for stx-lat-tool (regardless of cache status)
         # We always pass --build-context (even if empty) to keep Dockerfile compatible

stx/debian/bullseye/dockerfiles/stx-lat-tool.Dockerfile

@@ -1,4 +1,4 @@
-# syntax=docker/dockerfile:1
+# syntax=docker/dockerfile:1.4
 # Copyright (c) 2021,2025 Wind River Systems, Inc.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

stx/debian/trixie/dockerfiles/stx-lat-tool.Dockerfile

@@ -1,4 +1,4 @@
-# syntax=docker/dockerfile:1
+# syntax=docker/dockerfile:1.4
 # Copyright (c) 2021 Wind River Systems, Inc.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");