feat: Support legacy 'import' directive and use 'imports' for future

[smoser]

This changes the behavior of the 'import' target to behave as it did before the breaking change that moved imports into /stacker/imports/

So now, if the stacker file uses 'import', then imports will be placed in /stacker. If the stacker file uses 'imports' (plural) then they will be placed in /stacker/imports.

What we actually get in both cases is all the binds being done into either /.stacker (legacy) or /stacker (new). In the legacy case, the imports are also bind-mounted into /stacker

Legacy (for those that used 'import:')

 stacker: /.stacker/bin/stacker
 imports: /.stacker/imports -> /stacker
 runscript: /.stacker/imports/.stacker-run.sh
 artifacts: /.stacker/artifacts

new (for those that use 'imports:')

 stacker: /stacker/bin/stacker
 imports: /stacker/imports
 runscript: /stacker/imports/.stacker-run.sh
 artifacts: /stacker/artifacts

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Which issue does this PR fix:

What does this PR do / Why do we need it:

If an issue # is not available please add repro steps and logs showing the issue:

Testing done on this change:

Automation added to e2e:

Will this break upgrades or downgrades?

Does this PR introduce any user-facing change?:

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[smoser]

This wont work right now, I didn't adjust any of the tests, but this is the 'import -> /stacker' and 'imports -> /stacker/imports' change that I spoke with people about this week.

@mikemccracken , @hallyn , @rchincha

[rchincha]

Would also add a "Warning" that this is to be deprecated.

[smoser]

Would also add a "Warning" that this is to be deprecated.

done.

[codecov]

Codecov Report

Attention: 30 lines in your changes are missing coverage. Please review.

Comparison is base (a34ebfa) 53.57% compared to head (745b2bb) 54.29%.

Files	Patch %	Lines
pkg/stacker/bom.go	0.00%	10 Missing ⚠️
cmd/stacker/bom.go	0.00%	8 Missing ⚠️
pkg/stacker/build.go	77.77%	6 Missing and 2 partials ⚠️
pkg/types/layer.go	70.00%	2 Missing and 1 partial ⚠️
pkg/stacker/grab.go	87.50%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #543      +/-   ##
==========================================
+ Coverage   53.57%   54.29%   +0.71%     
==========================================
  Files          64       64              
  Lines        7473     7505      +32     
==========================================
+ Hits         4004     4075      +71     
+ Misses       2798     2737      -61     
- Partials      671      693      +22     

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[smoser]

@rchincha or @hallyn I'd appreciate feedback here.

This seems like a win to me. Basically

1. gets us backwards compatibility with "old stacker" (0.4.x) branch
2. makes stacker files more consistent. the following directives in a layer are all plural: overlay_dirs, volumes, labels, generate_labels, binds, annotations. import was singular, the change makes it plural going forward.
3. Allows users to move to newer stacker and move to new 'imports' lazily. the moves can even be done on one layer at a time (inside the same stacker file you can use 'import' for one layer and 'imports' for another). That reduces our need to maintain the 0.4.x branch.
4. cleans up the "binds" code a bit.

Note, it does break things that had moved to 1.0.0-rc5+ (where 'import' imported into /stacker/imports). Consumers moving from 1.0.0-rc5+ will have to change 'import:' to 'imports:' in stacker files. Consumers moving from < 1.0.0-rc5 should not need any changes.

Also note, we get a warning to console about deprecation of the 'import'. I would personally like to change that warning to put a stick in the mud saying "No stacker release after 2024-01-01 will support 'import'". That gives anyone picking this up a year to change and after that we can remove the old support.

[rchincha]

lgtm