The "payload" for the MQTT message.
In addition to environment variables and build parameters, the following variables can also be used (all variables must be encapsulated within "${}"):
- BUILD_RESULT - The result of the build (e.g. SUCCESS, FAILURE, ABORTED, etc.)
- PROJECT_URL - The job project's URL (e.g. "job/my-build")
- CULPRITS - Comma-separated list of the culprits responsible for the current build result
- BUILD_NUMBER - the build number