release pr/1.4.0

[aabmass]

• Release 1.4.0 (Part 1/2) release commit
• Release 1.4.0 (Part 2/2) bump version to 1.5.0

Made following https://github.com/GoogleCloudPlatform/opentelemetry-operations-python/blob/main/docs/releasing.md#run-release-script

• Make sure you review the the commits in the PR INDIVIDUALLY. The first commit (a) will be tagged as the release in the next step, so it needs to be correct.
• After review, merge your PR with "Rebase and merge" on github. This is crucial; if you use the regular "Squash and merge", you will not have the two sequential commits you need to create a release tag.