Social Notes: add option to set a default title format

[jeherve]

In combination with #42884 and #42293.

Right now, post titles are empty. Some folks would be interested in setting a default title, a bit like we do for the post list display in https://github.com/Automattic/jetpack/blob/aa40ce3cd63102932a16a2d61b3af886b020a6af/projects/plugins/social/src/class-note.php#L192-L205

It would be nice if we offered at least a filter that would allow folks to set a default title of their choice that would apply to all new notes.

• It could be "Daily note #xxx"
• It could use the date, as mentioned in this blog post

I sort of think the ability to give it a default post title appearance should be in the settings.

[BurakParsAydin]

Hi @jeherve I just created a PR. Would appreciate your feedback when you have a moment. Thanks!