add middleware version as image label

[gauron99]

Add the middleware-version image label to function images built by S2I and Pack builders to preserve complete the implementation. OCI already implements this (only added unit test since we can inspect the actual blobs/files created)

• label is only set when non-empty

1. func build --builder=s2i --push
2. Docker inspect...
3. Labels contain: "middleware-version": "v0.21.3",

PS:
some pack tests needed proper directory root because middleware fetch uses actual path detection for those templates (so it needs proper function root)

PSS: the s2i was added prior by Christoph but removed by me in the XXL scaffolding PR. Re-adding it here.

/kind enhancement
/fixes #3406

All function images now include the `middleware-version` label build by standard deployment

[codecov]

Codecov Report

❌ Patch coverage is 60.00000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 54.65%. Comparing base (7d24048) to head (542458f).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/buildpacks/builder.go	57.14%	2 Missing and 1 partial ⚠️
pkg/s2i/builder.go	62.50%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3408      +/-   ##
==========================================
+ Coverage   54.61%   54.65%   +0.04%     
==========================================
  Files         173      173              
  Lines       19814    19826      +12     
==========================================
+ Hits        10821    10836      +15     
+ Misses       7861     7857       -4     
- Partials     1132     1133       +1     

Flag	Coverage Δ
e2e	39.30% <60.00%> (+0.01%)	⬆️
e2e go	33.43% <60.00%> (+0.01%)	⬆️
e2e node	29.24% <60.00%> (+0.14%)	⬆️
e2e python	32.93% <30.00%> (-0.01%)	⬇️
e2e quarkus	29.39% <60.00%> (+0.16%)	⬆️
e2e rust	28.79% <10.00%> (+0.13%)	⬆️
e2e springboot	27.18% <30.00%> (+0.10%)	⬆️
e2e typescript	29.37% <60.00%> (+0.16%)	⬆️
integration	16.57% <0.00%> (+0.02%)	⬆️
unit macos-14	43.15% <60.00%> (+0.01%)	⬆️
unit macos-latest	43.15% <60.00%> (+0.01%)	⬆️
unit ubuntu-24.04-arm	43.47% <60.00%> (-0.01%)	⬇️
unit ubuntu-latest	44.06% <60.00%> (+0.01%)	⬆️
unit windows-latest	43.17% <60.00%> (+0.01%)	⬆️

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[matejvasek]

/approve
/lgtm

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: gauron99, matejvasek

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[creydr]

@gauron99 can we backport this fix to 1.21?

[gauron99]

/cherry-pick release-1.21

[knative-prow-robot]

@gauron99: new pull request created: #3410

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In response to this:

/cherry-pick release-1.21

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