Add tutorial extension to the docs

[ethanwharris]

What does this PR do?

Adds our turoial extension to enable compatibility with future updates to lightning tutorials.

Note: This doesn't change the docs in any way at this stage, just prevents an error that may occur when lightning tutorials is updated.

Does your PR introduce any breaking changes? If yes, please list them.

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Did you have fun?

Make sure you had fun coding 🙃

[tchaton]

LGMT !

[carmocca]

@ethanwharris should this be merged to a bug-fix release?

[ethanwharris]

@carmocca that would probably be safest as it's a totally backward compatible change 😃