Add support for platform API 0.7 and 0.8

[sambhav]

This PR adds support for 0.7 and 0.8.

Resolves #886

[codecov-commenter]

Codecov Report

Merging #889 (8907075) into main (5c07ecf) will increase coverage by 0.17%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #889      +/-   ##
==========================================
+ Coverage   68.08%   68.25%   +0.17%     
==========================================
  Files         116      116              
  Lines        5164     5192      +28     
==========================================
+ Hits         3516     3544      +28     
  Misses       1287     1287              
  Partials      361      361              

Impacted Files	Coverage Δ
pkg/cnb/builder_builder.go	84.07% <ø> (ø)
pkg/apis/build/v1alpha2/build_pod.go	98.19% <100.00%> (+0.07%)	⬆️

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[tylerphelan]

do we want to include the stack.toml or -run-image for analyze? https://github.com/buildpacks/spec/blob/main/platform.md#inputs (@natalieparellano)

[sambhav]

do we want to include the stack.toml or -run-image for analyze? buildpacks/spec@main/platform.md#inputs (@natalieparellano)

It's not needed for the way kpack builds things. It can just use the defaults (run image from stack.toml and stack.toml location as /cnb/stack.toml). We also never passed -stack in export before.

[matthewmcnew]

Do we want to also relax our mixin validation logic within that platform api?

[matthewmcnew]

Added an additional issue to track mixin validation relaxation: #891

[matthewmcnew]

I'd like to explore moving the instantiation of these containers within the pod spec (with the accepted possibility of some duplication). The step pattern was originally added to allow all the containers to be explicitly provided in the pod spec with some logic.

I think we can have something like:

if platformAPILessThan07 {
    step(detect...)
    step(analyze..)
}else {
    step(analyze...)
    step(detect..)
}
						

[matthewmcnew]

Happy to explore that in a future refactor though :)