Add clean-exclude input

This allows clients to ignore specific paths from the clean phase of the
checkout.

src/git-source-provider.ts

@@ -68,6 +68,7 @@ export async function getSource(settings: IGitSourceSettings): Promise<void> {
         settings.repositoryPath,
         repositoryUrl,
         settings.clean,
+        settings.cleanExclude,
         settings.ref
       )
     }