[chore][mdatagen] Add note about the supported types of telemetry metric attributes

[crobert-1]

Description

The context can be found here. Only a subset of attribute types are supported for telemetry metrics vs. regular metrics. There's no instrumentation equivalent for attributes of the type bytes, slice, and map.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.70%. Comparing base (2971358) to head (70ae615).
Report is 28 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #10997   +/-   ##
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  Coverage   91.70%   91.70%           
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  Files         411      411           
  Lines       19292    19292           
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  Hits        17692    17692           
  Misses       1239     1239           
  Partials      361      361           

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