fix: properly update 'label' field for helm + render w/ -l flag

[aaron-prindle]

Fixes #7336

Before this change:

aprindle@aprindle ~/skaffold/examples/helm-remote-repo  [fix-7336-add-label-helm-render]$ skaffold-v1.37.1 render --offline --digest-source=none --output=manifest.yaml -l=test=foo
--digest-source set to 'none', tags listed in Kubernetes manifests will be used for render
aprindle@aprindle ~/skaffold/examples/helm-remote-repo  [fix-7336-add-label-helm-render]$ cat manifest.yaml | grep foo
aprindle@aprindle ~/skaffold/examples/helm-remote-repo  [fix-7336-add-label-helm-render]$ 

After this change (the output shown is the change backported onto v1.37.1, currently there is no helm renderer in V2 IIUC. See - https://github.com/GoogleContainerTools/skaffold/blob/main/pkg/skaffold/render/renderer/noop/noop.go#L30):

aprindle@aprindle ~/skaffold/examples/helm-remote-repo  [fix-7336-add-label-helm-render]$ skaffold render --offline --digest-source=none --output=manifest.yaml -l=test=foo
--digest-source set to 'none', tags listed in Kubernetes manifests will be used for render
aprindle@aprindle ~/skaffold/examples/helm-remote-repo  [fix-7336-add-label-helm-render]$ cat manifest.yaml | grep foo
    test: foo
    test: foo
    test: foo
    test: foo
        test: foo
    test: foo
        test: foo

The changes for the V2 Helm -> Render method are nearly identical to what is done in V1. I understand in V2 this code is not used but the Helm deployer is TODO and IIUC likely re-using parts of the Render method will be done so it makes sense to get this in now so it will also be in the helm renderer implementation

[codecov]

Codecov Report

Merging #7349 (a7664f3) into main (290280e) will decrease coverage by 3.17%.
The diff coverage is 56.35%.

@@            Coverage Diff             @@
##             main    #7349      +/-   ##
==========================================
- Coverage   70.48%   67.31%   -3.18%     
==========================================
  Files         515      556      +41     
  Lines       23150    26589    +3439     
==========================================
+ Hits        16317    17898    +1581     
- Misses       5776     7410    +1634     
- Partials     1057     1281     +224     

Impacted Files	Coverage Δ
cmd/skaffold/app/cmd/credits/export.go	0.00% <0.00%> (ø)
cmd/skaffold/app/cmd/deploy.go	50.00% <0.00%> (-3.85%)	⬇️
cmd/skaffold/app/cmd/test.go	44.44% <0.00%> (ø)
cmd/skaffold/skaffold.go	0.00% <0.00%> (ø)
cmd/skaffold/app/cmd/render.go	36.66% <12.50%> (-4.72%)	⬇️
cmd/skaffold/app/cmd/inspect_tests.go	62.50% <14.28%> (-1.14%)	⬇️
cmd/skaffold/app/cmd/lsp.go	28.12% <28.12%> (ø)
cmd/skaffold/app/cmd/fix.go	54.09% <38.88%> (-22.38%)	⬇️
cmd/skaffold/app/cmd/lint.go	42.85% <42.85%> (ø)
cmd/skaffold/app/cmd/find_configs.go	48.88% <46.15%> (+0.24%)	⬆️
... and 272 more

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[MarlonGamez]

lgtm 👍🏼