User syndication options

Problem/Motivation

The users syndication options provided since 3.2.x are really great, but for our use-case of CH:

• All sites being publishers AND subscribers
• The editorial team is different on each site

We would need more options for user syndication.

We were previously just ignoring user syndication and the editors manually edited the node author after importing the node, but we think it would be a great improvement to provide another option for the user syndication were setting a "Proxy user" is not enough.

Proposed resolution

Provide an extra option when User syndication is disabled.

This new option would be something similar to:

• If node author exists on local site, use it as author (but prevent user syndication as we want to avoid changes on the user entity)
• If node author does not exist on local site, fallback to Anonymous user.

Remaining tasks

I'll create a MR for this issue so CH engineers can take a look and evaluate if you want to include this on the contrib module (and probably add some tests to the new options).