Update changelog for new release 4.0.0 #2650

Job	Run time
build-python-wheels (ubuntu-20.04, auto64)	27m 12s
build-and-push-docker-images	22m 58s
build-python-wheels (macos-11, auto64)	34m 47s
build-and-test-cpp-aarch64 (openblas)	3m 55s
build-and-test-cpp-x86_64 (ubuntu-20.04, mkl)	5m 53s
build-python-wheels (windows-2019, auto64)	40m 34s
build-python-wheels (ubuntu-20.04, aarch64)	1h 11m 30s
build-and-test-cpp-x86_64 (ubuntu-20.04, dnnl)	5m 15s
check-python-style	7s
build-python-wheels (macos-11, arm64)	11m 30s
build-and-test-cpp-x86_64 (macos-11, mkl)	9m 38s
build-and-test-cpp-x86_64 (macos-11, dnnl)	9m 4s
build-and-deploy-docs	30s
test-python-wheels (ubuntu-20.04)	11m 48s
test-python-wheels (macos-11)	4m 12s
test-python-wheels (windows-2019)	4m 23s
publish-python-wheels-on-pypi	0s
	4h 23m 16s

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