Add code-block to example responses in generate_rst.py

[vicferpoy]

Hi team.

Since the web-team added a new block to make outputs more appealing (https://github.com/wazuh/wazuh-documentation/pull/2084), we needed to update our generate_rst.py script in order to implement these new blocks.

Every Example response has this structure now:

**Example Response:**
.. code-block:: json
    :class: output
    {
       "error": 0,

Regards.