Decide what to do with perl5/perl6 in filenames

[JJ]

The problem

"5" and "6" appear in the migration documents.

Suggestions

Instead of just moving the files, delete its content and make them point to the new filename. Or create redirects, but I don't like solutions that depend on the tooling and configuration.

[AlexDaniel]

Definitely a redirect is needed, but yeah, perl-to-raku is a better name.

[coke]

(from the linked ticket: We will probably need to find incoming links to them too, even external ones, but we can always solve that with a redirect.)

[JJ]

@coke I would very much prefer to leave the old pages, unchanged, with a notice to the new ones. Right now all the site is working statically, without redirects (well, roughly...). All additional tooling might complicate it beyond what's necessary.
We can always dig up external links and tell them. Don't really think there should be too many of them (but if there are, redirect would probably be the best option)