Fix issue where custom JSOn serializer generates Base64 encoded data in state store

[abogdanov37]

Description

Refactor ObjectSerializer class to add ability set custom object mapper.
Refactor DaprStateAsyncprovider class to use custom serializers based on ObjectSerializer class as Json serializer.
Add unit tests.

Issue reference

#503

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• Code compiles correctly
• Created/updated tests
• Extended the documentation

[artursouza]

Please, use the DaprObjectSerializer interface to bring your own serializer. The default serializer is just for examples and getting started.

[artursouza]

Please, focus on fixing the issue where a custom JSON serializer becomes Base64 encoded. Making DefaultObjectSerializer is a controversial change since it is not supposed to be used outside examples or getting started with Dapr.

[abogdanov37]

Please, focus on fixing the issue where a custom JSON serializer becomes Base64 encoded. Making DefaultObjectSerializer is a controversial change since it is not supposed to be used outside examples or getting started with Dapr.

Ok. I will revert changes with ObjectSerializer and focused on the issue. Thanks for your feedback.

[codecov]

Codecov Report

Merging #504 (51b44be) into master (a5051e0) will not change coverage.
The diff coverage is 33.33%.

@@            Coverage Diff            @@
##             master     #504   +/-   ##
=========================================
  Coverage     80.43%   80.43%           
+ Complexity      975      974    -1     
=========================================
  Files            88       88           
  Lines          3015     3015           
  Branches        331      330    -1     
=========================================
  Hits           2425     2425           
  Misses          424      424           
  Partials        166      166           

Impacted Files	Coverage Δ	Complexity Δ
...io/dapr/actors/runtime/DaprStateAsyncProvider.java	60.86% <33.33%> (ø)	13.00 <0.00> (-1.00)

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[artursouza]

We can make this check even more extensible by having a deeper understanding of different media types. This change is already an important improvement.