[Access] Make response for data providers consistent.

[AndriiDiachuk]

Closes: #6819

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 56.70732% with 142 lines in your changes missing coverage. Please review.

Project coverage is 41.02%. Comparing base (8ff124c) to head (e549056).

Files with missing lines	Patch %	Lines
...e/access/rest/common/models/mock/link_generator.go	14.37%	129 Missing and 2 partials ⚠️
engine/access/rest/router/router.go	0.00%	5 Missing ⚠️
engine/access/rest/http/routes/blocks.go	70.00%	3 Missing ⚠️
.../rest/websockets/data_providers/blocks_provider.go	83.33%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6846      +/-   ##
==========================================
- Coverage   41.19%   41.02%   -0.17%     
==========================================
  Files        2109     2079      -30     
  Lines      185664   182029    -3635     
==========================================
- Hits        76479    74677    -1802     
+ Misses     102777   101100    -1677     
+ Partials     6408     6252     -156     

Flag	Coverage Δ
unittests	41.02% <56.70%> (-0.17%)	⬇️

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[Guitarheroua]

I do not have any other comments. Looks good!