fix: only load required delegantions

[phbelitz]

When using delegation for nv1, Connaisseur now only loads those delegation files it actually needs for verification and not all available.

fixes #171

[codecov-commenter]

Codecov Report

Merging #318 (ec9e6ed) into develop (e45fb1a) will decrease coverage by 0.09%.
The diff coverage is 87.50%.

@@             Coverage Diff             @@
##           develop     #318      +/-   ##
===========================================
- Coverage    96.65%   96.56%   -0.10%     
===========================================
  Files           22       22              
  Lines         1077     1076       -1     
===========================================
- Hits          1041     1039       -2     
- Misses          36       37       +1     

Impacted Files	Coverage Δ
...naisseur/validators/notaryv1/notaryv1_validator.py	94.95% <87.50%> (-0.88%)	⬇️

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[Starkteetje]

There should be a test to highlight and ensure the functional diff

[Starkteetje]

Commit has delegantions, other than that lgtm

[phbelitz]

OKOKOK. I had to change the code a bit after adding additional tests and realizing that there were some bugs... so the last commit adds 3 tests:

1. checking behavior when a delegation is required, that doesn't exist (didn't had to change the code for that).
2. checking behavior when a delegation is required (e.g. del1) + the targets.json also has said delegation listed, but the actual file (e.g. targets/del1.json) is missing (had to change the code).
3. checking behavior when no delegations are required, the targets.json says it theoretically has delegation (even though not required), but the delegation files themselves are missing. this corresponds to a very rare edge case, where delegations are added to a repo, but no signatures were yet created using these delegations. normally we would use the targets/releases.json file, but since this file doesn't exists yet, we have to use the targest.json instead (had to change the code again).

[Starkteetje]

Nice one catching the regression