apple-llvm-config: add pr.json config for git-apple-llvm pr tool

Author: hyp

apple-llvm-config/pr.json

@@ -0,0 +1,9 @@
+{
+"type": "github",
+"domain": "github.com",
+"user": "apple",
+"repo": "llvm-project",
+"test": {
+    "type":"swift-ci"
+}
+}