cli: accept snap file in legacy upload-metadata command

[merlijn-sebrechts]

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fxes: https://bugs.launchpad.net/snapcraft/+bug/1995857

The legacy upload-metadata command didn't have a location argument for the snap file itself. This PR adds that argument, and fixes some issues with the hacking doc and environment setup.

$snapcraft upload-metadata signal-desktop_5.57.0_amd64-core18.snap
Usage: snapcraft [options] command [args]...
Try 'snapcraft upload-metadata -h' for help.

Error: unrecognized arguments: signal-desktop_5.57.0_amd64-core18.snap

[merlijn-sebrechts]

What is not clear to me, is why snapcraft push-metadata uses the path via upload.py and snapcraft upload-metadata uses the path via legacy.py.

[codecov-commenter]

Codecov Report

Merging #3975 (0bdb35e) into main (5799b03) will decrease coverage by 0.02%.
The diff coverage is 0.00%.

❗ Current head 0bdb35e differs from pull request most recent head f58b549. Consider uploading reports for the commit f58b549 to get more accurate results

@@            Coverage Diff             @@
##             main    #3975      +/-   ##
==========================================
- Coverage   91.04%   91.02%   -0.03%     
==========================================
  Files          56       56              
  Lines        4086     4087       +1     
==========================================
  Hits         3720     3720              
- Misses        366      367       +1     

Impacted Files	Coverage Δ
snapcraft/commands/legacy.py	79.41% <0.00%> (-0.79%)	⬇️

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[sergiusens]

Thanks for this.
Sorry for the delay.

The reason for the split is moslty due to not having moved this functionality to the new cli