Update #cache example code on Render API overview to use Node::getCacheTags instead of hard coding

Problem/Motivation

API page: https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Render%21...

The documentation for the Render API overview contains the following example code demonstrating how to use #cache with a render array.

Here's an example of what a #cache property might contain:

  '#cache' => [
    'keys' => ['entity_view', 'node', $node->id()],
    'contexts' => ['languages'],
    'tags' => ['node:' . $node->id()],
    'max-age' => Cache::PERMANENT,
  ],

I believe that this line 'tags' => ['node:' . $node->id()], should be 'tags' => $node->getCacheTags() instead. This demonstrates the best practice of using ::getCacheTags() for the entity instead of trying to memorize all possible cache tags you would need to include here.

I was personally getting hung up on trying to figure out what valid values for 'tags' would be. And I believe the answer is, I should haven't to know that because I can just use ::getCacheTags() for anything that implements \Drupal\Core\Cache\CacheableDependencyInterface

Proposed resolution

Update the code in documentation to use $node->getCacheTags() instead of the current example.

Remaining tasks

Update the docs.

API changes

None

Data model changes

None