Rebaser changes for run image extension

[jabrown85]

• Add --force flag to rebase command
• Validate io.buildpacks.rebasable label on rebase
• Read rebase from io.buildpacks.lifecycle.metdata runImage

Open Questions

1. Should the runImage not be present, should we be failing? The spec doesn't say it allows for the fallback to the old stack key..but it feels aggressive to me.
2. The spec says specifically to fail is the value of rebaseable is false. I coded it as such, but anything other than false is treated as true. This may be unexpected.

Ref: #1000

[natalieparellano]

Should the runImage not be present, should we be failing? The spec doesn't say it allows for the fallback to the old stack key..but it feels aggressive to me.

I think we should fall through to the stack key. Otherwise it would be hard to rebase old apps that were created before the platform was upgraded.

[jabrown85]

Should the runImage not be present, should we be failing? The spec doesn't say it allows for the fallback to the old stack key..but it feels aggressive to me.

I think we should fall through to the stack key. Otherwise it would be hard to rebase old apps that were created before the platform was upgraded.

I agree. Do we need a spec change then? Rebase spec doesn't say this will happen.

[natalieparellano]

Do we need a spec change then? Rebase spec doesn't say this will happen.

Sounds good. I made a code suggestion here: https://github.com/buildpacks/spec/pull/335/files#r1142221664 on buildpacks/spec#335

[natalieparellano]

@jabrown85 this one looks fully updated - should we merge it?

[jabrown85]

I'm happy if you are @natalieparellano! No one has reviewed it officially so go right ahead 😄

[natalieparellano]

Looks great!