"blob" materializer task

[sandreae]

Introduces a new "blob" task to the materializer service which:

• is issued once a dependency task finishes on a blob_v1 or blob_piece_v1 document
• if the document in question is part of a completed blob (all dependencies met, this isn't always true when a blob_piece_v1 document triggered the "blob" task) then we persist the blob view to the filesystem at the expected path ../<blob_document_id>/<blob_view_id>
• we also create a symlink from the expected path to the blob when served by it's document id ../documents/<blob_document_id>`.

Next steps

• would be good to have a blob module which contains all io stuff

📋 Checklist

• Add tests that cover your changes
• Add this PR to the Unreleased section in CHANGELOG.md
• Link this PR to any issues it closes
• New files contain a SPDX license header

[codecov]

Codecov Report

Patch coverage: 6.03% and project coverage change: +0.26% 🎉

Comparison is base (81cae95) 91.20% compared to head (1633382) 91.47%.

❗ Current head 1633382 differs from pull request most recent head c2a0a36. Consider uploading reports for the commit c2a0a36 to get more accurate results

Additional details and impacted files

@@               Coverage Diff               @@
##           development     #493      +/-   ##
===============================================
+ Coverage        91.20%   91.47%   +0.26%     
===============================================
  Files              101      102       +1     
  Lines            16393    16353      -40     
===============================================
+ Hits             14952    14959       +7     
+ Misses            1441     1394      -47     

Files Changed	Coverage Δ
aquadoggo/src/config.rs	46.80% <0.00%> (+11.88%)	⬆️
aquadoggo/src/materializer/tasks/blob.rs	0.00% <0.00%> (ø)
aquadoggo/src/materializer/service.rs	94.76% <100.00%> (+0.01%)	⬆️
aquadoggo/src/materializer/tasks/dependency.rs	97.56% <100.00%> (+0.02%)	⬆️

... and 3 files with indirect coverage changes

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[adzialocha]

Great! Looking all good.

I would consider adding our own routes and handlers for the /blobs paths. Both for MIME types and helping with the symlinking workaround. I'm fine to handle this in a separate PR though.