Add examples for new grpc endpoints

[illia-malachyn]

Closes: #784

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 57.03%. Comparing base (9f84549) to head (476bb37).
Report is 9 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #794      +/-   ##
==========================================
- Coverage   57.04%   57.03%   -0.01%     
==========================================
  Files          35       35              
  Lines        7391     7392       +1     
==========================================
  Hits         4216     4216              
- Misses       2673     2674       +1     
  Partials      502      502              

Flag	Coverage Δ
unittests	57.03% <ø> (-0.01%)	⬇️

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[illia-malachyn]

I get a nil pointer dereference exception when running the send-and-subscribe-transaction-statuses example. The cause might be hidden in the method implementation in flow-go repo. I will open an issue for this.

What's more, the stream-account-statuses example doesn't work due to this issue onflow/flow-go#6575