Gradle task avoidance api should be used consistently in the build

[breskeby]

At several places in the gradle build we still see usage of the old task creation api. This should be replaced by using the task avoidance api of gradle (tasks.register(...){}).

This makes the build more consistent and eventually gives us slightly better configuration time. Though this step alone might not result in many task creations being avoided yet as this also requires some further optimisations in how existing tasks are requested within the build scripts and different plugins. This will addressed later on in a different issue.

Update: Many tasks have been converted. Two major remainings:

• RestIntegTest tasks are created eagerly. Tasks of type RestIntegTest created during task graph calculation causes

1. the creation of clusters late after all build scripts have been evaluated.
2. distributions late in the build after the current setupDistribution (see https://github.com/elastic/elasticsearch/blob/master/buildSrc/src/main/java/org/elasticsearch/gradle/DistributionDownloadPlugin.java#L82)

One fix for 1) would be, to configure test clusters that are created by a RestIntegTest in the context of the task like:

tasks.named('integTest').configure {
   testclusters.integTest {
       // test cluster configuration
   }
}

The benefit of this is that the test cluster configuration would only happen if the cluster is required by the build.

Fixing 2) is more complex as we need to find a different solution for delaying the distribution setup. We can probably replace the afterEvaluate usage by using configuration.defaultDependencies{} hooks

[elasticmachine]

Pinging @elastic/es-core-infra (:Core/Infra/Build)