The plugin is bundled since TeamCity 10.0. The recent version is described in the online documentation for the latest TeamCity version.
Allows publishing a commit status to an external system. Supported are GitHub, Atlassian Bitbucket Server (formerly Stash), Gerrit Code Review.
Once the plugin is installed, add the Commit Status Publisher build feature to your build configuration.
Compatible with TeamCity 9.1+.
Get the plugin artifact from a recent successful build on the TeamCity public server:
TeamCity 9.1 compatible version
Sources at github.
Issues in TeamCity issue tracker.