fix(examples): replace phpinfo() with hello world in php examples

The php and php-zip examples called phpinfo() in index.php, which renders
the full PHP environment — including the Lambda-injected AWS_ACCESS_KEY_ID,
AWS_SECRET_ACCESS_KEY, and AWS_SESSION_TOKEN — to anyone hitting the public
endpoint. Users following the examples as-is would expose their function's
temporary execution-role credentials.

Replace the phpinfo() call with a plain-text "Hello, World!" response and
update the php-zip README verification step accordingly.

Author: bnusunny

examples/php-zip/README.md

@@ -23,4 +23,4 @@ When the deployment completes, take note of URL's Value. It is the API Gateway e
 
 ### Verify it works
 
-Open URL's URL in a browser, you should see `phpinfo()` on the page. 
+Open URL's URL in a browser, you should see `Hello, World!` on the page. 

examples/php-zip/app/public/index.php

@@ -2,4 +2,6 @@
 
 require __DIR__ . '/../vendor/autoload.php';
 
-phpinfo();
+header('Content-Type: text/plain');
+
+echo "Hello, World!";

examples/php/app/public/index.php

@@ -2,4 +2,6 @@
 
 require __DIR__ . '/../vendor/autoload.php';
 
-phpinfo();
+header('Content-Type: text/plain');
+
+echo "Hello, World!";