Pluto notebooks for tutorials: CI doesn't update dependencies in embedded Manifest.toml

[pwochner]

When building the docs with CI, we activate the Julia environment using dependencies in docs/Project.toml to run + build the notebooks. This makes sure that the latest version of the dependencies are used.

The dependencies embedded at the end of Pluto tutorial notebooks (PLUTO_MANIFEST_TOML_CONTENTS) however are not updated by the CI. This potentially leads to a situation where all notebooks are run successfully by the CI, but might fail when a user opens and runs a notebook from the REPL (since Pluto will install all required packages based on the information in PLUTO_MANIFEST_TOML_CONTENTS).

[pwochner]

Adding this code cell at the top of a Pluto notebook

begin
	import Pkg
	Pkg.activate(Base.current_project())
	Pkg.instantiate()
end

disables Pluto's built-in package manager. This way, we can make sure that the same environment is used by the CI and when running the notebook interactively.

There are functions that modify the embedded dependencies of notebook directly. But then we either need to run them and commit the changes manually, or add it to the CI and make sure the CI commits the changes to the repo.

[ReubenJ]

I think this fix makes sense. Nice and simple!