Move from wpslugs extension to using a flow to generate slugs

[freekrai]

Discussed in https://github.com/freekrai/directed-stack/discussions/4

^{Originally posted by freekrai October 7, 2022} Currently, we use the wpslugs extension to generate slugs, this means deploying to Directus cloud is limited.

To improve support for everywhere, and to make use of the great Flows Data Studio, I want to switch this to use Flows rather than an extension to generate the slugs. This is the Flow I generally use now, and will be adding to the site, as I move away from including the slugs extension.

This also means adding a flows step to the docs as well.