statestore query API: remove 'value' prefix from key names in query JSON

[dmitsh]

Description

statestore query API: remove 'value' prefix from key names in query JSON object

Issue reference

We strive to have all PR being opened based on an issue, where the problem or feature have been discussed prior to implementation.

Please reference the issue this PR will close: #1490

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 / Created issue in the https://github.com/dapr/docs/ repo: dapr/docs#[issue number]

[codecov]

Codecov Report

Merging #1491 (716f9d2) into master (625f955) will increase coverage by 0.00%.
The diff coverage is 88.88%.

@@           Coverage Diff           @@
##           master    #1491   +/-   ##
=======================================
  Coverage   35.29%   35.29%           
=======================================
  Files         157      157           
  Lines       14241    14242    +1     
=======================================
+ Hits         5026     5027    +1     
  Misses       8692     8692           
  Partials      523      523           

Impacted Files	Coverage Δ
bindings/mysql/mysql.go	46.89% <0.00%> (ø)
state/azure/cosmosdb/cosmosdb_query.go	55.05% <100.00%> (ø)
state/mongodb/mongodb_query.go	40.00% <100.00%> (ø)
state/postgresql/postgresql_query.go	59.18% <100.00%> (+0.42%)	⬆️

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