feat: async image validation

[phbelitz]

Connaisseur now validates all images in side a single request in parallel.

fixes #226

[codecov-commenter]

Codecov Report

Merging #334 (c5a6a18) into develop (f4b0728) will decrease coverage by 0.15%.
The diff coverage is 87.17%.

@@             Coverage Diff             @@
##           develop     #334      +/-   ##
===========================================
- Coverage    96.65%   96.49%   -0.16%     
===========================================
  Files           22       22              
  Lines         1077     1085       +8     
===========================================
+ Hits          1041     1047       +6     
- Misses          36       38       +2     

Impacted Files	Coverage Δ
connaisseur/flask_server.py	92.92% <84.84%> (-1.58%)	⬇️
connaisseur/validators/cosign/cosign_validator.py	98.61% <100.00%> (ø)
connaisseur/validators/interface.py	100.00% <100.00%> (ø)
...naisseur/validators/notaryv1/notaryv1_validator.py	95.83% <100.00%> (ø)
...naisseur/validators/notaryv2/notaryv2_validator.py	80.00% <100.00%> (ø)
connaisseur/validators/static/static_validator.py	93.75% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update f4b0728...c5a6a18. Read the comment docs.