Add check on CI to compare more files

[jtpio]

Follow-up to #119

Starting from JupyterLab 3.0 extensions can now be installed via pip, which is the way described in these examples.

New files have been added to each example, such as setup.py, MANIFEST.in and pyproject.toml:

https://github.com/jupyterlab/extension-examples/tree/ab5aefa454408b5cc6155c89eed8cc4db641c564/basics/hello-world

One way to check they are all in sync would be to run the upgrade script as mentioned in #119 (comment)

Similar to this step:

extension-examples/.github/workflows/main.yml

Lines 45 to 50 in e7054af

	- name: Check config files
	run: |
	diff basics/hello-world/tsconfig.json ${EXAMPLE_FOLDER}/tsconfig.json
	diff basics/hello-world/.eslintignore ${EXAMPLE_FOLDER}/.eslintignore
	diff basics/hello-world/.eslintrc.js ${EXAMPLE_FOLDER}/.eslintrc.js
	diff basics/hello-world/.gitignore ${EXAMPLE_FOLDER}/.gitignore