Make developers more aware of the need for create-extension

[Sebastian-ubs]

User Story
As a extension developer, I want to know I need to run create-extension so that I can do this early

As a core developer, I want extension developers to run create-extension so that I do not have more effort helping them to make their extension maintainable later

Description
As not running create-extension to create and extension requires some rework later, make people aware of it initially - even if they did not read the docs. Those people would think the can just copy an existing extension and do some replacements, which seems to work running npm run start but would later cause issues with updating the extension.

See https://github.com/paranext/platform-bible-sample-extensions?tab=readme-ov-file#to-create-a-new-extension-in-this-repo

Implementation idea
Idea:

• Detect that create-extension has not run, based on ... git? ...
• Have npm run start fail with a suitable error message in this case

Testing ideas

1. Create a new extension by copying an existing one in a multi extension template, e.g. platform-bible-sample-extensions
2. Watch that npm run start fails in this case
3. Follow the link provided in the error message to create a new extension by running npm run create-extension -- <extension_name>
4. Watch that npm run start succeeds in this case