fix: Add deprecation warning for path property when creating pages

gatsby-node.js

@@ -96,19 +96,24 @@ exports.createPages = async ({ actions, graphql, reporter }) => {
       });
     }
 
-    if (frontmatter.path !== slug) {
-      const newPath = path.join(
+    if (frontmatter.path) {
+      const recommendedPath = path.join(
         'src/markdown-pages',
         fileRelativePath.endsWith('index.mdx')
           ? path.join(frontmatter.path, 'index.mdx')
           : `${frontmatter.path}.mdx`
       );
 
-      reporter.error(
+      const recommendation =
+        recommendedPath === fileRelativePath
+          ? "Please remove the 'path' property."
+          : `To render this page at '${frontmatter.path}', please move this file to: '${recommendedPath}'.`;
+
+      reporter.panicOnBuild(
         `
-File path does not match frontmatter path:
-  mkdir -p ${path.dirname(newPath)}
-  mv ${fileRelativePath} ${newPath}
+${fileRelativePath}
+
+The 'path' property on frontmatter is deprecated and has no effect. URLs are now generated using the path of the file. ${recommendation}
 `.trim()
       );
     }