RFC: `pack stack create`

[jromero]

Description

Based on this RFC, pack should implement a new command using the upcoming tool stackify.

pack stack create

Proposed solution

See pack references under "How it Works" in the RFC.

Describe alternatives you've considered

Additional context

• Blocked by availability of stackify tool (TBD)

[jromero]

No longer applicable due to stacks going away as per buildpacks/rfcs#172.