refactor: rename 'layer' as 'image' in stacker publish path

[rchincha]

What type of PR is this?

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.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (2152d8d) 57.17% compared to head (96038a0) 57.17%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #583   +/-   ##
=======================================
  Coverage   57.17%   57.17%           
=======================================
  Files          64       64           
  Lines        7521     7521           
=======================================
  Hits         4300     4300           
  Misses       2479     2479           
  Partials      742      742           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[hallyn]

Seems the right thing to do, but are there any users that will get broken by this?

[mikemccracken]

Seems the right thing to do, but are there any users that will get broken by this?

I am not aware of any in our internal usage, just looked. I think there is a lot of just 'skopeo copy'ing going on in scripts that predate or were ignorant of 'stacker publish'.