Configure Gradle User Home for dependency-graph

Instead of requiring an action step to generate the graph, configure Gradle User Home
so that subsequent Gradle invocations can generate a graph. Any generated graph files
are uploaded as artifacts on job completion.

- Construct job.correlator from workflow/job/matrix
- Export job.correlator as an environment var
- Upload artifacts at job completion in post-action step
- Specify the location of dependency graph report
- Only apply dependency graph init script when explicitly enabled

src/resources/init-scripts/github-dependency-graph-gradle-plugin-apply.groovy

@@ -0,0 +1,6 @@
+buildscript {
+  dependencies {
+    classpath files("github-dependency-graph-gradle-plugin-0.0.3.jar")
+  }
+}
+apply plugin: org.gradle.github.GitHubDependencyGraphPlugin