Remove the Multiplexer Tutorial

[bilgeyucel]

Describe the issue
Multiplexer tutorial has been hidden for some time already. We now need to remove the tutorial and redirect the link to the tutorial overview page by adding a redirect in haystack-home repo.

Additional context
N/A

[kacperlukawski]

@bilgeyucel I created two PRs in both repositories, not sure if I should assign them directly to you for a review?