Provide input parameters for key environment variable supported by GitHub Dependency Graph plugin

[bigdaz]

Currently, there are some key configuration inputs to the GitHub Dependency Graph plugin that can only be provided via environment variables. The full list is here, here and here.

We don't need to support all of these variables, since some are set by the action and there's little or no reason to override them. We also only need to support these for dependency-submission. When setup-gradle with dependency-graph enabled, users can continue to provide environment variables.

For now, we should at least provide:

• report-dir: DEPENDENCY_GRAPH_REPORT_DIR with paths resolved relative to the project workspace
• exclude-projects: DEPENDENCY_GRAPH_EXCLUDE_PROJECTS
• exclude-configurations: DEPENDENCY_GRAPH_EXCLUDE_CONFIGURATIONS
• Possibly the 'include' variations as well.

For now we can leave out the variables that control the 'runtime' scope, since these are largely experimental. Ideally, the plugin would make a good guess at the dependencies that are in runtime scope, but it's not trivial.