Log a warning when log Record attribute is dropped

[MrAlias]

Fix #5317

According to the specification, there should be a message printed in the SDK's log to indicate to the user that an attribute was discarded due to such a limit. To prevent excessive logging, the message must be printed at most once per LogRecord (i.e., not per discarded attribute).

This change centralizes the Record dropped field writes and calls a global logging function. This will at most log once per any Record dropping attributes, meeting the specification requirement.

This does not log once per Record when an attribute is dropped. To do that we would need to maintain state within the Record (i.e. sync.Mutex or sync.Once). These types cannot be copied, meaning the Record would take on this "no copy" requirement. This seems too restrictive and with the permissive specification allowing a single log line, that is the solution added.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.5%. Comparing base (515d2c4) to head (111adce).

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #5376   +/-   ##
=====================================
  Coverage   84.5%   84.5%           
=====================================
  Files        268     268           
  Lines      17808   17818   +10     
=====================================
+ Hits       15064   15074   +10     
  Misses      2430    2430           
  Partials     314     314           

Files	Coverage Δ
sdk/log/record.go	100.0% <100.0%> (ø)