Fix #8860: doc: Usage of recipe directive is wrong

The pre check in the `ReceipeDirective.add_target_and_index() was wrong.
It checkes non-existing option "noindex", but it should check "contains"
option instead.

I missed that there are actually two sections explaining extensions in the docs and just saw the examples based one. This lead to me thinking "kind of lousy documentation, but that's probably par for the course". Would there have been a pointer to the detailed extension API description it would have saved me hours of guesswork.

Keep imports alphabetically sorted and their order homogeneous across
Python source files.

The isort project has more feature and is more active than the
flake8-import-order plugin.

Most issues caught were simply import ordering from the same module.
Where imports were purposefully placed out of order, tag with
isort:skip.