Extend --artifact API schema to allow for manifest generation

[MarlonGamez]

Fixes: #6249, #6248

Description
CC: @briandealwis @j-windsor

Users can now generate manifests using the --artifact (or -a) flag by passing some additional information in their json objects.

The schema changes are as follows:
Before:

{
  "builder": string,
  "payload": {
    "path": string,
  },
  "image": string,
},

After:

{
  "builder": string,
  "payload": {
    "path": string,
  },
  "image": string,
  "manifest-info:": {
    "path": string,
    "port": int,
  },
}

Follow-up Work
Document this feature

[codecov]

Codecov Report

Merging #6599 (f6178c3) into main (290280e) will decrease coverage by 0.14%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##             main    #6599      +/-   ##
==========================================
- Coverage   70.48%   70.34%   -0.15%     
==========================================
  Files         515      517       +2     
  Lines       23150    23326     +176     
==========================================
+ Hits        16317    16408      +91     
- Misses       5776     5853      +77     
- Partials     1057     1065       +8     

Impacted Files	Coverage Δ
cmd/skaffold/app/cmd/flags.go	90.81% <ø> (ø)
cmd/skaffold/skaffold.go	0.00% <ø> (ø)
pkg/skaffold/build/buildpacks/logger.go	0.00% <ø> (ø)
pkg/skaffold/config/options.go	100.00% <ø> (ø)
pkg/skaffold/debug/apply_transforms.go	22.64% <0.00%> (-0.44%)	⬇️
pkg/skaffold/debug/transform.go	95.91% <ø> (ø)
pkg/skaffold/docker/logger/log.go	22.64% <0.00%> (-0.44%)	⬇️
pkg/skaffold/initializer/build/builders.go	42.85% <0.00%> (-17.15%)	⬇️
pkg/skaffold/initializer/build/util.go	94.44% <0.00%> (-5.56%)	⬇️
pkg/skaffold/kubectl/exec.go	100.00% <ø> (ø)
... and 45 more

---

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[nkubala]

code generally looks good, one question about the ports