- Adds a getWebhooks method/endpoint to the Reclaim interface for
querying the customizable webhooks.
- Adds the observer that runs when a product is saved.
- Adds the Cron class for managing product data that needs to be synced
to Klaviyo.
- Admin HTML for configuring the webhook.
- Modify the webhook helper so we only encode the json once.

- Remove some comments.
- Reduce if statements to a single line.

- Move store_ids to top level property.

- In the observer we'll just get the cateroy ids.
- In the cron job we'll look up the category names based on the ids so
this code runs in the background instead of when the user is saving a
product.

- Change the response from the getWebhooks endpoint so that it returns
an array of arrays instead of an array of associative arrays. This makes
it unpackable app-side.