pack should support platform 0.10

[natalieparellano]

Changes needed:

• Declare platform API 0.10 as supported
• Set CNB_EXPERIMENTAL_MODE=warn in the lifecycle's execution environment
• Invoke the restorer with the -build-image flag and cache volume mounted at /kaniko (when there are extensions)
• Invoke the extender binary with the builder image digest reference as the first argument and cache volume mounted at /kaniko (when there are extensions)
• Invoke the exporter as usual
• pack inspect <image with 0.9 buildpacks> should succeed (with existing codebase it shows ERROR: unable to find image 'hello-extensions' locally or remotely)

Out of scope (need separate issues):

• The --extension equivalent of --buildpack
• Support for extensions in project.toml
• pack build with extensions and --cache-image (adds complexity as it requires managing both a cache image and a cache volume; kaniko always needs a volume)
• pack build with extensions and a local (only) builder (because kaniko needs a manifest for the builder image, the builder must be pushed to a registry; would require a re-implementation of the extender in pack that uses the docker daemon instead of kaniko, or an extender lifecycle binary that can use the daemon socket)

[natalieparellano]

On further reflection, -analyzed and -buildpacks aren't configurable with pack today, so maybe it's okay if we don't pass the flags and let everything fall back to the default value.

If we're okay with the lifecycle emitting warnings, maybe there is nothing to do here.

[natalieparellano]

At a minimum, the supported platform apis will need to be updated to include 0.10.

[natalieparellano]

This should also be resolved by #1478

[natalieparellano]

Update: #1478 will be updated to remove "platform 0.10 support". Also, the lifecycle will FAIL if CNB_EXPERIMENTAL_MODE is unset, so pack will need to set this variable when --experimental is used.