Add ability to use package json version.

This will only work with top level package json file and not nested files.

src/main.ts

@@ -73,6 +73,18 @@ function resolveVersionInput(): string {
     );
   }
   
+  if (version === "package") {
+    const packageJson = JSON.parse(
+      fs.readFileSync(
+        path.join(
+          process.env.GITHUB_WORKSPACE!, 
+          "package.json"
+        )
+      )
+    );
+    return packageJson.engines.node;
+  }
+
   if (version) {
     return version;
   }