This commit upgrades the default CNB builder image from
cloudfoundry/cnb:0.0.43-bionic to cloudfoundry/cnb:0.0.53-bionic.
It also adds integration tests for the Maven and Gradle plugins
to verify both versions are supported.
This documentation moves the specific `build-image` execution
configuration example of the Maven plugin documentation to the general
plugin configuration. This makes sure that it works in most cases and
an execution-specific configuration is not required here anyway.
Closes gh-19946
Scott Frederick
Phillip Webb
Stephane Nicoll