Added tests for blobs

[bart-degreed]

As it turns out, using blobs already works nicely using base64 encoding. This PR just adds tests for that.

Closes #1108.

QUALITY CHECKLIST

• Changes implemented in code
• Complies with our contributing guidelines
• Adapted tests
• N/A: Documentation updated
• N/A: Created issue to update Templates: {ISSUE_NUMBER}

[codecov]

Codecov Report

Merging #1125 (4dd636e) into master (9c9a4f2) will increase coverage by 0.06%.
The diff coverage is 82.98%.

❗ Current head 4dd636e differs from pull request most recent head 5e7bd9b. Consider uploading reports for the commit 5e7bd9b to get more accurate results

@@            Coverage Diff             @@
##           master    #1125      +/-   ##
==========================================
+ Coverage   89.41%   89.48%   +0.06%     
==========================================
  Files         245      241       -4     
  Lines        7294     7198      -96     
==========================================
- Hits         6522     6441      -81     
+ Misses        772      757      -15     

Impacted Files	Coverage Δ
...NetCoreExample/Controllers/NonJsonApiController.cs	0.00% <0.00%> (ø)
...NetCoreExample/Controllers/OperationsController.cs	0.00% <0.00%> (ø)
...ples/JsonApiDotNetCoreExample/Data/AppDbContext.cs	0.00% <0.00%> (ø)
...otNetCoreExample/Definitions/TodoItemDefinition.cs	0.00% <0.00%> (ø)
...Examples/JsonApiDotNetCoreExample/Models/Person.cs	0.00% <0.00%> (ø)
...rc/Examples/JsonApiDotNetCoreExample/Models/Tag.cs	0.00% <0.00%> (ø)
...amples/JsonApiDotNetCoreExample/Models/TodoItem.cs	0.00% <0.00%> (ø)
src/Examples/JsonApiDotNetCoreExample/Program.cs	0.00% <0.00%> (ø)
...Core/AtomicOperations/MissingTransactionFactory.cs	0.00% <0.00%> (ø)
...sonApiDotNetCore/Diagnostics/CascadingCodeTimer.cs	0.00% <0.00%> (ø)
... and 353 more

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