Add metadata attribute to DataSetDefinition

[samantha-ho]

This PR adds a metadata attribute to the DataSetDefinition class used with the measurement extension datasaver_builder

Metadata that is included in the DataSetDefinition is automatically added to datasets/datasavers created via the datasaver_builder

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69.37%. Comparing base (f88415f) to head (71eb451).
Report is 41 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6643   +/-   ##
=======================================
  Coverage   69.37%   69.37%           
=======================================
  Files         340      340           
  Lines       31293    31300    +7     
=======================================
+ Hits        21708    21715    +7     
  Misses       9585     9585           

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