return array of pointers in get account keys for consistency

[illia-malachyn]

Closes: #783

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 28.57143% with 5 lines in your changes missing coverage. Please review.

Project coverage is 56.59%. Comparing base (38ecc3c) to head (2f7fa8b).
Report is 9 commits behind head on master.

Files with missing lines	Patch %	Lines
access/grpc/convert/convert.go	0.00%	3 Missing ⚠️
access/grpc/client.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #792      +/-   ##
==========================================
- Coverage   57.03%   56.59%   -0.45%     
==========================================
  Files          35       35              
  Lines        7392     7305      -87     
==========================================
- Hits         4216     4134      -82     
+ Misses       2674     2670       -4     
+ Partials      502      501       -1     

Flag	Coverage Δ
unittests	56.59% <28.57%> (-0.45%)	⬇️

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