Exposing client operator with a getter

[rokn]

Description:
This PR exposes the client operator for easier access, to enable signing arbitrary data with it.

Checklist

• Documented (Code comments, README, etc.)
• Tested (unit, integration, etc.)

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (3ce2e32) 77.02% compared to head (b859319) 76.49%.
Report is 3 commits behind head on develop.

❗ Current head b859319 differs from pull request most recent head 6a09bf5. Consider uploading reports for the commit 6a09bf5 to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1970      +/-   ##
===========================================
- Coverage    77.02%   76.49%   -0.53%     
===========================================
  Files          265      304      +39     
  Lines        66273    75800    +9527     
===========================================
+ Hits         51048    57986    +6938     
- Misses       15225    17814    +2589     

Files	Coverage Δ
src/token/AssessedCustomFee.js	82.46% <100.00%> (+30.33%)	⬆️
src/token/TokenWipeTransaction.js	92.73% <100.00%> (+11.33%)	⬆️
src/transaction/TransactionRecord.js	91.98% <100.00%> (+18.23%)	⬆️
src/client/Client.js	83.04% <71.42%> (-0.11%)	⬇️

... and 195 files with indirect coverage changes

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