Refactor notebooks (#7752)

* drop notebooks

* add submodule

* copy notebooks

* docs include ipynb

* fix headers

* CI

* readthedocs

* manifest

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* req

* workdir

* pandoc

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* pandoc

* manifest

* Apply suggestions from code review

* fix versions

* checkout

* `git submodule update --init --recursive --remote`

* notebooks @docs

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>