Add pitest dependencies only during configuration resolution; resolves #302

[omalleyian]

Changes the adding of dependencies to the pitest configuration to use the withDependencies method, and moves the addition of dependencies to occur during plugin configuration instead of task configuration.

I ran into the same error reported by #302 when using the VSCode vscode-gradle extension (3.10.0+), and I believe that the issue is caused by the pitest configuration (probably all configurations) being resolved during the project configuration phase - before this plugins' tasks add their dependencies. The intent of my changes are to wrap this plugin's dependency additions in a configuration action that will be executed whenever the pitest configuration is resolved - whether by the pitest task or some other reason (vscode-gradle plugin or project-report).

Fixes the issue when using both the project-report plugin and the VSCode vscode-gradle extension.

[szpak]

Looks good. Thanks for your contribution.