Add get account keys endpoints

[illia-malachyn]

Closes: #744

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 60.00000% with 24 lines in your changes missing coverage. Please review.

Project coverage is 52.41%. Comparing base (b87f9c7) to head (8884ba7).
Report is 7 commits behind head on master.

Files with missing lines	Patch %	Lines
access/grpc/client.go	0.00%	8 Missing ⚠️
access/grpc/convert/convert.go	0.00%	8 Missing ⚠️
access/grpc/grpc.go	81.81%	4 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #753      +/-   ##
==========================================
+ Coverage   51.45%   52.41%   +0.96%     
==========================================
  Files          35       35              
  Lines        5446     5506      +60     
==========================================
+ Hits         2802     2886      +84     
+ Misses       2288     2240      -48     
- Partials      356      380      +24     

Flag	Coverage Δ
unittests	52.41% <60.00%> (+0.96%)	⬆️

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[illia-malachyn]

@janezpodhostnik you can merge it

[franklywatson]

Can merge once conflicts are resolved