build: publish release script should add release notes to tag

[devversion]

• Adds the release notes to the release tag. This can be also used in the future to create the Github release through the API.

Blocked on #14595

[jelbourn]

LGTM

[devversion]

I tried to think about a more efficient way and initially used a read stream since the changelog file can technically become huge over the years, but that was just so much overhead, so I just went with the simple approach.

[jelbourn]

We should move all the pre 5.0.0 stuff to another file at some point

[devversion]

👍

[ngbot]

I see that you just added the pr: merge ready label, but the following checks are still failing:
     status "branch-manager" is failing
     status "ci/circleci: tests_local_browsers" is pending
     status "ci/circleci: tests_browserstack" is pending
     status "ci/circleci: tests_saucelabs" is pending
     status "ci/circleci: bazel_build_test" is pending
     status "ci/circleci: build_release_packages" is pending
     status "ci/circleci: e2e_tests" is pending
     status "ci/circleci: prerender_build" is pending
     status "ci/circleci: lint" is pending
     status "ci/circleci: api_golden_checks" is pending

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If you can't get the PR to a green state due to flakes or broken master, please try rebasing to master and/or restarting the CI job. If that fails and you believe that the issue is not due to your change, please contact the caretaker and ask for help.

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