Checkstyle aggregate

[srnagar]

• Maven goal checkstyle:checkstyle is not inherited from the reactor parent and hence is using the default checkstyle rules for each of the child modules which means that failsOnError is false.
• Maven goal checkstyle:checkstyle-aggregate works as expected and fails the build if any of the child modules have checkstyle errors
• To use the parent pom's checkstyle configuration in a multi-module project like ours, we have to use maven goal site as per this documentation - https://maven.apache.org/plugins/maven-checkstyle-plugin/examples/multi-module-config.html

So, we have the following options:

1. If we have to use checkstyle:checkstyle we need to duplicate the configuration in each of the child modules.
2. We can instead use checkstyle:checkstyle-aggregate which will accomplish what we want
3. Continue to use site:site site:stage

For the purpose of failing the PR build with minimum amount of work, we will use checkstyle:checkstyle-aggregate (option 2 above).