Error boundaries

[slorber]

💥 Proposal

There's no getDerivedStateFromError or componentDidCatch in Docusaurus v2.

Errors might not happen very often, particularly most of them would simple make the build fail.

But it might still be useful to add a default global error boundary in case the code of the user produces a runtime error. Some people might introduce buggy code in pages that might crash at runtime.

[spyke01]

I'll take a look into this.