chore: switch to SPDX license headers#5177

MikeGoldsmith wants to merge 4 commits intoopen-telemetry:mainopen-telemetry/opentelemetry-python:mainfrom

MikeGoldsmith:mike/spdx-license-headersMikeGoldsmith/opentelemetry-python:mike/spdx-license-headersCopy head branch name to clipboard