fix: change amplify to ampx (#7729)

Author: magisystem0408

src/pages/[platform]/reference/cli-commands/index.mdx

@@ -17,8 +17,8 @@ export const meta = {
   /**
    * Notes for documentation:
    * - only document 2 command levels deep. document further levels in the top-level command as usage examples but without additional subheading
-   *   - (good) amplify sandbox secret
-   *   - (bad) amplify sandbox secret set
+   *   - (good) ampx sandbox secret
+   *   - (bad) ampx sandbox secret set
    * - all commands should describe:
    *   - what the command is and when it is used
    *   - unordered list of options