Byline on new post isn't auto-populated if the sidebar panel is closed

[dlh01]

Description of the bug

The REST API request to hydrate profiles runs when the document sidebar is open and the "Summary" panel is expanded. This REST request includes the logic to automatically set the profile associated with the current user as the byline of a post (see #56). If the "Summary" panel is collapsed or the document sidebar is closed when a post is created, the REST request never runs, and the current user isn't assigned as the post's byline.

Steps To Reproduce

1. Create a Byline Manager profile, and link it to your WordPress user account.
2. Create and save a new post with the document sidebar open and the "Summary" panel expanded, and observe that the linked profile is set as the byline.
3. Close the document sidebar, create and save a new post, and observe that the post has no assigned byline.

Additional Information

No response