docker: Fix a bug where images with port number and no tags weren't parsed correctly

[vincentDcmps]

Description

when using private registry without any image tag pull get Invalid reference format issue

Testing & Reproduction steps

on version 1.9.4 send a job with image with following format:

ghcr.service.consul:5000/paperless-ngx/paperless-ng

Reviewer Checklist

• Backport Labels Please add the correct backport labels as described by the internal
  backporting document.
• Commit Type Ensure the correct merge method is selected which should be "squash and merge"
  in the majority of situations. The main exceptions are long-lived feature branches or merges where
  history should be preserved.
• Enterprise PRs If this is an enterprise only PR, please add any required changelog entry
  within the public repository.

[hashicorp-cla-app]

All committers have signed the CLA.

[vincentDcmps]

Hi does something is missing in this PR to be review?

[vincentDcmps]

could I have a feeback on this PR? I supose i'm not alone to use private registry?

[pkazmierczak]

Hi @vincentDcmps, thanks a lot for the PR and apologies it took a while for anyone to take a look at it. Code looks good to me, I only left a formatting suggestion. Would you also mind adding a small changelog entry? You can make it with make cl, something like:

docker: Fix a bug where images with port number and no tags weren't parsed correctly.

Then I'm happy to merge.

[pkazmierczak]

LGTM! Thanks, @vincentDcmps!