Check for an existing image before processing media on the target site.

[iamdharmesh]

Description of the Change

As reported in #765, when the same image is used in multiple posts and these posts are distributed to connected sites, the media files are imported for each post, creating duplicate copies of the images on the target sites. This PR fixes the media duplication issue by checking for existing media on the target site before creating new media.

Closes #765

How to test the Change

1. Assign the same image file to multiple posts on the origin site.
2. Distribute these posts to a subsite (network connection) or external connection.
3. Verify that there are no duplicate images on the target site and that images are reused in multiple posts.

Changelog Entry

Changed - The default value of the filter dt_sync_media_delete_and_replace has been updated from true to false.
Fixed - Resolved the media duplication issue when the same image is used in multiple posts.

Credits

Props @philbraun @jeffpaul @iamdharmesh

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added Critical Flows, Test Cases, and/or End-to-End Tests to cover my change.
• All new and existing tests pass.

[peterwilsoncc]

This looks good to me and tests well, thanks.

Just a minor note inline to include the data provider param annotations in the test's docblock. Otherwise I think it's good to go.

[peterwilsoncc]

Thanks for the follow up, this looks good to merge.