Logging for 404 and 500 errors

[Altai-man]

We want to log 404 errors to add redirects wherever usable and 500 errors to fix bugs.

Technically it is just extending handlers at https://github.com/Altai-man/docs.raku.org/blob/master/lib/Docky/Routes.pm6#L26-L29 with something writing a log somewhere where it is nicely visible. Potentially with squashing duplicated errors? Something fancy is welcome.

The redirect checking will be more interesting in case of superseding the original docs website, but we need to have it structured sooner than that.

[Altai-man]

Kind of blocked by croservices/cro-http#131