feat: add digest to artifacts info of published docker images

[gal-legit]

Extract the digest (sha256) of docker images from the docker push command for dockers published to the docker registry.
Outputting the digest is required to avoid a race condition when referencing the image, where the image tag is being modified before the reference is done.
See this blog post for more info.
This PR fixes #3496.

Note that the 'publish' pipe now must run before the 'metadata' pipe, so that the information extracted during the 'publish' pipe would appear in the metadata.
Previously, the published docker images metadata wasn't printed (because of the order). It made sense because the content of the published image was just a subset of the local one.
Now that it is printed to the metadata, it should have a different name to avoid confusion.
As I mentioned, it wasn't printed before - so there shouldn't be any backward-compatibility issues.

---

Local tests:

go test -v .
=== RUN   TestVersion
=== RUN   TestVersion/only_version
=== RUN   TestVersion/version_and_date
=== RUN   TestVersion/version,_date,_built_by
=== RUN   TestVersion/all_empty
=== RUN   TestVersion/complete
--- PASS: TestVersion (0.00s)
    --- PASS: TestVersion/only_version (0.00s)
    --- PASS: TestVersion/version_and_date (0.00s)
    --- PASS: TestVersion/version,_date,_built_by (0.00s)
    --- PASS: TestVersion/all_empty (0.00s)
    --- PASS: TestVersion/complete (0.00s)
PASS
ok      github.com/goreleaser/goreleaser        0.764s

Output example:

  {
    "name": "gallegit/hello-world:latest",
    "path": "gallegit/hello-world:latest",
    "goos": "linux",
    "goarch": "amd64",
    "internal_type": 10,
    "type": "Published Docker Image",
    "extra": {
      "digest": "sha256:c3f7dd196a046dc061236d3c6ae1e2946269e90da30b0a959240ca799750e632"
    }
  }

[codecov]

Codecov Report

Merging #3540 (5965c86) into main (778f099) will increase coverage by 0.00%.
The diff coverage is 85.71%.

@@           Coverage Diff           @@
##             main    #3540   +/-   ##
=======================================
  Coverage   83.63%   83.64%           
=======================================
  Files         116      116           
  Lines        9656     9692   +36     
=======================================
+ Hits         8076     8107   +31     
- Misses       1280     1284    +4     
- Partials      300      301    +1     

Impacted Files	Coverage Δ
internal/artifact/artifact.go	84.91% <0.00%> (-0.61%)	⬇️
internal/pipe/docker/api_docker.go	88.23% <70.00%> (-5.10%)	⬇️
internal/pipe/docker/api.go	100.00% <100.00%> (ø)
internal/pipe/docker/docker.go	91.32% <100.00%> (+0.13%)	⬆️

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[caarlos0]

hey @gal-legit ! this looks awesome! Thank you!

can you cherry-pick this commit? d389030

so we ensure this is not broken at some point :)

[gal-legit]

@caarlos0 done. Thanks for the feedback! :)

[caarlos0]

awesome, thank you @gal-legit !