Update semconv to 1.21.0, PART 5 - Imports

[trask]

Splitting #9370 this up into smaller pieces for review. Once the parts are approved, I will merge them into a single PR, with one commit per part, and send any additional final commits if needed to make CI happy.

for file in $(git ls-files)
do
  sed -i 's/io\.opentelemetry\.semconv\.trace\.attributes\.SemanticAttributes/io.opentelemetry.semconv.SemanticAttributes/g' $file
  sed -i 's/io\.opentelemetry\.semconv\.resource\.attributes\.ResourceAttributes/io.opentelemetry.semconv.ResourceAttributes/g' $file
done

git checkout -- *.png

[laurit]

Superseded by #9408