Ability to change the name of the "title" field in Joplin

### [Add user story here] As a content editor...

`Title` is a shared field across all content types. In #3625, we wanted the ability to change `Title` to `Location name` for the location content type, but we don't want to cause a regression on other content types. We might also want to customize other things in the future, like `Event title`.

Start by reading issue #3625 and locating how the shared Title field is defined for Joplin content types. No file or test is named in this issue. Done means a content type can use a custom label such as “Location name” without changing the label for other content types.

Written by the indexing model from the issue text.