Add hook to filter WP_Query args for get_pull_content REST endpoint

[theskinnyghost]

Description of the Change

This PR introduces a new hook which can be used to filter the arguments used by WP_Query in the distributor/list-pull-content REST API endpoint (based on existing hook provided by WP core, see rest_this-post_type_query).

This can be useful to filter down the content when users have already pulled content from a connection.

Alternate Designs

N/A

Possible Drawbacks

I guess there could be a possible negative performance impact if a developer doesn't use the filter properly (e.g. setting posts_per_page to -1).

Verification Process

I did add a custom mu-plugin plugin to my WP install with the following code and was able to change the results for the WP_Query.

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests passed.

Changelog Entry

Added - New hook to filter WP_Query args for the list-pull-content REST endpoint