feat(content-distribution): partial payload

[miguelpeixe]

Implements support for distribution of partial payloads, given a list of post data keys to include in the payload.

The Content_Distribution::distribute_post_partial( $post, $post_data_keys ) can be called directly to trigger a partial update, but it should be most commonly used in the context of distribute_queued_posts(), which will decide on PHP shutdown whether to execute a partial or full distribution of a given post, based on the contents of the $queued_distributions var, populated via the queue_post_distribution( $post_id, $post_data_key ); method.

E.g., if a post is saved and a post meta is updated in the same execution, the following will be called:

Content_Distribution::queue_post_distribution( <post_id> ); // via wp_after_insert_post hook
Content_Distribution::queue_post_distribution( <post_id>, 'post_meta' ); // via updated_post_meta hook

The above will trigger a single full post update on shutdown.

If only a post meta is updated on the execution:

Content_Distribution::queue_post_distribution( <post_id>, 'post_meta' ); // via updated_post_meta hook

A single partial update will run on shutdown.

This PR also improves the post meta coverage by hooking into added_post_meta and deleted_post_meta.

Testing

1. Distribute a post to a node
2. Update a post meta via CLI wp post meta update {post_id} test_meta test_value
3. Confirm in the hub's event log that the payload's post data only includes post_meta, date_gmt, and modified_gmt
4. Delete the post meta via CLI wp post meta delete {post_id} test_meta
5. Confirm in the hub's event log table that the payload includes the post_meta and test_meta is not there
6. In the dashboard, edit the post and save
7. Confirm in the hub's event log that the full payload is sent

[naxoc]

Tested this and it works great. Thanks!

I only added a small nit on return type.

[naxoc]

The error should be returned here I think –not a string.

[miguelpeixe]

Good catch! Fixed in ac91081

[github-actions]

Hey @miguelpeixe, good job getting this PR merged! 🎉

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