Release google-api-java-client v1.28.0 (googleapis#1233)

* Release v1.28.0

* Fix dependency for google-http-client-apache and Apache transport

* Fix promote/drop kokoro configs

Release google-api-java-client v1.27.0 (googleapis#1214)

* Release v1.27.0

* bom needs developers section and release config/profile

Release v1.26.0 (googleapis#1193)

* Release v1.26.0

* Actually use the nexus-staging-maven-plugin

* Fix leftover snapshot versions in assembly

* Fix snapshot version in assembly

Add plugin configuration to maven-release-plugin

Add plugin configuration to maven-release-plugin

Add plugin configuration to maven-release-plugin

Add plugin configuration to maven-release-plugin

Add plugin configuration to maven-release-plugin

Merge pull request googleapis#934 from google/release-1.20.0

Release 1.20.0

Add plugin configuration to maven-release-plugin