Update README and samples/pom.xml (googleapis#555)

Release 1.28.0/0.45.0 (googleapis#546)

bump version for release (googleapis#544)

bump version for release (googleapis#531)

Release 1.25.0/0.42.0 (googleapis#528)

bump version to 1.24.0 and 0.41.0 (googleapis#523)

Release 1.23.0 (googleapis#519)

Release version to 1.22.0/0.39.0 (googleapis#516)

Bump version to 1.21.0/0.38.0 (googleapis#505)

Bump version to 1.20.0/0.37.0 (googleapis#499)