Add the timestamp field to the PAI request

Problem/Motivation

For my project, I need to fetch the media creation date, AKA the 'timestamp' field.

Proposed resolution

This can be done in the getUserMedia() function in src/InstagramBasicDisplayApi.php file as:

$fields = !empty($fields) ? $fields : [
  'id', 'caption', 'media_url', 'media_type', 'thumbnail_url',
  'permalink', 'timestamp',
];

Patch is attached.

For informations, other fields seem to be available from the API (not tested):

• id
• ig_id
• media_product_type
• media_type
• media_url
• thumbnail_url
• timestamp
• username
• like_count
• comments_count

Remaining tasks

Will try to find time to open a MR