fix: handle image references with both a tag and digest present

[chgl]

Fixes #749

Description

It is possible for image references to contain both a tag and a digest at the same time. Previously, this was not handled causing the validators to fail.

I'm not sure if what I did is the most idiomatic or even elegant Python, but the changes are at least fairly small.

I've built and pushed the image as ghcr.io/chgl/connaisseur:fix-image-tag-and-digest and testet it using the helm chart by setting

deployment:
  image: ghcr.io/chgl/connaisseur:fix-image-tag-and-digest

The images that were previously causing issues were now correctly validated and accepted.

Checklist

• PR is rebased to/aimed at branch develop
• PR follows Contributing Guide
• Added tests (if necessary)
• Extended README/Documentation (if necessary)
• Adjusted versions of image and Helm chart in values.yaml and Chart.yaml (if necessary)

[chgl]

Draft as long as there is no consensus on whether or not this is actually the right approach in #749

[phbelitz]

@richgerrard with this the tag is preserved and should be visible in the k8s pod description. additionally, what might be possible to do is add the tag and digest as annotations to the mutated resource. that might be more convenient to get information about the resource, without the need to do additional parsing. is that something you deem as useful?

[codecov-commenter]

Codecov Report

Base: 96.90% // Head: 96.94% // Increases project coverage by +0.04% 🎉

Coverage data is based on head (5ed6c9b) compared to base (00b6d2a).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #763      +/-   ##
===========================================
+ Coverage    96.90%   96.94%   +0.04%     
===========================================
  Files           22       22              
  Lines         1226     1244      +18     
===========================================
+ Hits          1188     1206      +18     
  Misses          38       38              

Impacted Files	Coverage Δ
connaisseur/flask_application.py	93.75% <100.00%> (ø)
connaisseur/image.py	100.00% <100.00%> (ø)
...naisseur/validators/notaryv1/notaryv1_validator.py	98.36% <100.00%> (+0.04%)	⬆️

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