What does this Pull Request do?

This PR adds a filter to the http_request() function in class Object_Sync_Sf_Salesforce to allow short-circuiting the API call and response.

The goal of the PR is to help create a tighter integration with WP Fusion (https://github.com/verygoodplugins/wp-fusion-lite/ and https://wpfusion.com/).

The logic follows what already exists in WP core, for example with update_metadata(): https://github.com/WordPress/WordPress/blob/master/wp-includes/meta.php#L233

With this filter in place, we will be able to:

• Route outgoing API calls through WP Fusion (and the WordPress HTTP API / wp_remote_request())
• Use WP Fusion's built in error handling, logging, and token refresh capabilities for Object Sync API calls
• Detect potential data collision (for example if WP Fusion is about to operate on the same record)
• Automatically configure Object Sync using the Salesforce client ID and tokens already managed by WP Fusion

We're excited to create a deeper integration between WP Fusion and Object Sync for Salesforce, and this change would allow us to tie the two plugins together much more closely than is currently possible.

Thanks for your consideration :)