Automatically update the created date for talks

Automatically update the created dates for talk nodes so that they match
the most-future event. This means that the talks are ordered correctly
on the Talks page.

phpstan.neon

@@ -7,6 +7,9 @@ parameters:
     - *Test.php
     - *TestBase.php
   checkMissingIterableValueType: false
+  ignoreErrors:
+    - '#Call to an undefined method Drupal\\Core\\Entity\\EntityInterface::get()#'
+    - '#Call to an undefined method Drupal\\Core\\Entity\\EntityInterface::set()#'
 includes:
   - vendor/mglaman/phpstan-drupal/extension.neon
   - vendor/phpstan/phpstan-deprecation-rules/rules.neon