We previously were recording the Schema URL but were not setting
the recorded value when exporting. This change now uses the recorded
value when exporting to OTLP.
* Removed DroppedAttributeCount field from Link struct
* Reintroduced DroppedAttributeCount with a wrapper struct
* Added Link type in otel/sdk package and used it instead of Trace API equivalent
* Added changelog entry
* Linting fix in changelog
* Deleted duplicated changelog section added by mistake
* Expanded changelog entry and moved it under the 'Added' section
* Explicitly mentioned otel/trace library in changelog entry under 'Removed' section to avoid ambiguity
