introduce publish (alpha) command

[ndeloof]

What I did
introduce publish command - this is just command skeleton, backend is missing an implementation

Related issue
this is skeleton code toward a publish command to implement compose-spec/compose-spec#288
https://docker.atlassian.net/browse/ENV-249

(not mandatory) A picture of a cute animal, if possible in relation to what you did

[codecov]

Codecov Report

Patch coverage: 32.25% and project coverage change: -0.21% ⚠️

Comparison is base (0be8e4a) 58.94% compared to head (12cdac7) 58.73%.

Additional details and impacted files

@@            Coverage Diff             @@
##               v2   #10815      +/-   ##
==========================================
- Coverage   58.94%   58.73%   -0.21%     
==========================================
  Files         120      122       +2     
  Lines       10453    10484      +31     
==========================================
- Hits         6161     6158       -3     
- Misses       3696     3725      +29     
- Partials      596      601       +5     

Files Changed	Coverage Δ
pkg/api/api.go	42.30% <ø> (ø)
pkg/compose/publish.go	0.00% <0.00%> (ø)
pkg/api/proxy.go	39.19% <33.33%> (-0.09%)	⬇️
cmd/compose/publish.go	47.05% <47.05%> (ø)
cmd/compose/alpha.go	100.00% <100.00%> (ø)

... and 3 files with indirect coverage changes

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[ndeloof]

Pushed to https://github.com/docker/compose/tree/publish so we can iterate on implementing this feature