Add support for "dataset" messages

[mraspaud]

This PR adds support for "dataset" messages.

[codecov]

Codecov Report

Attention: Patch coverage is 89.47368% with 2 lines in your changes missing coverage. Please review.

Project coverage is 89.07%. Comparing base (649820d) to head (b24bc53).
Report is 69 commits behind head on master.

Files	Patch %	Lines
trolldb/cli.py	71.42%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master       #8      +/-   ##
==========================================
+ Coverage   88.82%   89.07%   +0.25%     
==========================================
  Files          24       24              
  Lines         832      842      +10     
==========================================
+ Hits          739      750      +11     
+ Misses         93       92       -1     

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