I ran the linkcheck builder of the 4.4 docs and fixed all broken or permanently redirected links. Most of them are about moving to HTTPS.

We can't run the linkcheck builder automatically:

• Some docs use permanent redirects to redirectcurrent to a specific version (seems really bad). We want to keep using "current" here
• In a similair way, some sites allow i18n if you omit the locale from the URL, these are also permanently redirected
• I don't want us to spam all the links every time GitHub actions runs :)

Also note that Doctrine switched the "latest" version to Doctrine ORM 3.0. I've changed all these to "current" (i.e. 2.6 atm) instead.