feat: Added support of alternative S3 storage

[frgfm]

This PR adds support for alternative S3 storage interfaces, and refactors QarnotBucket as an S3Bucket. Additionally, this PR improves the media upload route:

• previously, we uploaded the file, then downloaded it to check that the hash is identical (1 upload + 1 download)
• with this PR, we upload the file, then only read the MD5 hash computed by S3 file system (1 upload) This should speed up the route while decreasing bandwidth requirements.

Any feedback is welcome!

[codecov[bot]]

Codecov Report

Merging #220 (fb06278) into master (e4edd58) will increase coverage by 0.55%. The diff coverage is 60.93%.

@@            Coverage Diff             @@
##           master     #220      +/-   ##
==========================================
+ Coverage   93.52%   94.07%   +0.55%     
==========================================
  Files          46       47       +1     
  Lines        1281     1282       +1     
==========================================
+ Hits         1198     1206       +8     
+ Misses         83       76       -7     

Flag	Coverage Δ
unittests	94.07% <60.93%> (+0.55%)	:arrow_up:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/app/services/bucket/s3.py	45.65% <45.65%> (ø)
src/app/api/routes/media.py	86.84% <100.00%> (+3.29%)	:arrow_up:
src/app/api/security.py	100.00% <100.00%> (ø)
src/app/config.py	94.28% <100.00%> (+0.73%)	:arrow_up:
src/app/services/bucket/__init__.py	100.00% <100.00%> (ø)
src/app/services/bucket/qarnot.py	100.00% <100.00%> (+49.15%)	:arrow_up:

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