Rewrite links in all imported docs

[dholbach]

@aryan9600 says

while doing an overview of our docs, i discovered that the link to Provider in this section doesn’t work, probably because the actual file is out of tree from the perspective of the website folder. should we just hardcode the link instead? https://fluxcd.io/flux/components/notification/alert/#provider-reference

One way to go about this would be to teach hack/gen-content.py to import from "latest release". It knows how to rewrite links. cf https://github.com/fluxcd/website/blob/main/hack/gen-content.py