chore: Update react / cypress / slate / toast & more

[demshy]

Summary
A major overhaul of dependencies and required changes in code+tests to adapt to the new library versions. There are obviously a lot of changes and I will try to make a summary here of what was done as well as what was intentionally left out for the next phase (and why).
This version is currently deployed in a private repo and undergoing internal testing with some of our bigger sites where we used as much of the cms functionalities as possible. We are already aware of some bugs, that will be listed below.

Upgraded libraries

• react 16 -> 18
• typecript 3 -> 4
  Fixed some minor typing inconsistencies but nothing big.
• webpack 4 -> 5
  Not many changes needed apart from some configuration files
• lerna 4 -> 6
  Lerna 6 now uses nx task runner and a lot of scripts for running, building and testing the project had to be adapted. File change watching is now done by Lerna instead of webpack and react-hot-loader was removed (we might need to find an alternative for this?)
• cypress 9 -> 12
  Needed to adapt the e2e tests for some of the things the new version does differently. Some updated snapshots, some stuff that worked in previous version, but shouldn't have and some stability hacks for slate to be tested properly. There were some suggestions among the community to consider Playwright as a Cypress replacement and i would gladly explore this after this PR.
• slate 0.4 -> 0.9
  This was the biggest and most time (and nerve) consuming update because it is basically a rewrite of the whole implementation https://docs.slatejs.org/concepts/xx-migrating
  Luckily the serializers were split into two parts - slate>remark>markdown so only slate>remark part needed adaptations. There were a lot of slate plugins that needed work - lists being the most problematic. We were relying on cypress e2e tests to ensure everything works as before but also the tests needed some adaptations to play nice with the new version.

Replaced libaries
Some libraries that are no longer maintained needed to be replaced with alternatives.

• redux-notifications > react-toastify
  One of the first things that we did because redux-notifications is unmaintained and outdated
• react-sortable-hoc -> @dnd-kit/sortable
  Sortable elements are not working as they were supposed to after upgrading React. As the react-sortable-hoc github suggests, we moved to the suggested solution. It is already implemented on file lists, but might be a bit more complicated with relations, because it uses react-select and migrating is not as straight forward as it seems: Update the Sortable Multiselect component documentation JedWatson/react-select#5212

Todo

• copy/paste in slate editor
• apply dnd-kit/sortable to lists and relations
• review peerDependencies and make the repo play nice with yarn 1.22 Failed to install dependencies in workspace: expected workspace package to exist yarnpkg/yarn#7807
• figure out why the website build is failing
• review the release process and prepare a RC

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