Make it possible to use build docker image using BuildKit

As per Docker release 18.09 it is possible to mount cache (using BuildKit) explained

Example dockerfile

# syntax = docker/dockerfile:1.0-experimental

#RUN --mount=type=cache,target=/home/gradle/.gradle gradle build

However when build such image, it is gives an error

Dockerfile parse error line 12: Unknown flag: mount

Code to build:

new GenericContainer<>(
                new ImageFromDockerfile()
                                .withDockerfile(Path.of("Dockerfile").toAbsolutePath())
        )

I order to build such docker image from CLI, you need to set DOCKER_BUILDKIT=1 in order to use buildkit.

While analyzing docker cli source code it seems like it is appending such query parameter to REST API call version=2

• Prepare build parameters
  https://github.com/docker/cli/blob/master/cli/command/image/build_buildkit.go#L207
• sending request via client
  https://github.com/docker/cli/blob/b350e14b1f83e1870a234ff2c554450707218204/vendor/github.com/docker/docker/client/image_build.go#L136

Unfortunately, I do not see any documented version parameters in the official API documentation.
https://docs.docker.com/engine/api/v1.40/#operation/ImageBuild

issue で言及されている ImageFromDockerfile のビルドパスと Docker client の ImageBuild リクエストから始め、次に Docker CLI がどのように BuildKit を有効化し、version=2 を渡しているかを比較します。そのパラメーターに対する Docker API の動作を確認します。提供された RUN --mount を使用する Dockerfile が GenericContainer 経由で Unknown flag エラーなしに正常にビルドできれば完了です。