Add support for dockerfile/1.3.0

[darkdragon-001]

Actual behavior
New features from dockerfile/1.3.0 are not available (1, 2)

• RUN command allows --network flag for requesting a specific type of network conditions. --network=host requires allowing network.host entitlement. This feature was previously only available on labs channel. Documentation
• ADD command with a remote URL input now correctly handles the --chmod flag. Fix file modes with remote ADD commands moby/buildkit#2171
• Values for RUN --mount flag now support variable expansion, except for the from field feat(run-mount): add support for variable expansion moby/buildkit#2089
• Allow BUILDKIT_MULTI_PLATFORM build arg to force always creating multi-platform image, even if only contains single platform Support BUILDKIT_MULTI_PLATFORM arg in Dockerfile moby/buildkit#1985
• RUN and COPY commands now support Here-document syntax allowing writing multiline inline scripts and files Dockerfile heredocs moby/buildkit#2132 Improve progress and history messages for heredoc-related commands moby/buildkit#2201 Add support for heredocs in the ONBUILD command moby/buildkit#2209 Improve heredoc parsing to allow more generic shell-words moby/buildkit#2213 Documentation

Expected behavior
Feature parity with docker.

To Reproduce
Steps to reproduce the behavior:
Try to build a Dockerfile with 1.3.0 syntax.

Additional Information

• Dockerfile
• Build Context
• Kaniko Image (fully qualified with digest)

Triage Notes for the Maintainers

Description	Yes/No
Please check if this a new feature you are proposing
Please check if the build works in docker but not in kaniko
Please check if this error is seen when you use --cache flag
Please check if your dockerfile is a multistage dockerfile

[guillaume-d]

Well, dockerfile/1.2.0 is not available either, see #1568. So this bug depends on that being fixed too/first.