[Feature]: Add ability to handle same-origin external links

[JounQin]

What problem does this feature solve?

We have multiple document projects, and we want to link each other with simple markdown link syntax, but currently all links starting with slash are considered in current document project which results unexpected behavior.

We can not use http:// like links because those websites are expected to be deployed under multiple hostnames. IPs, domains, etc.

What does the proposed API look like?

Add a new option like externalLinkPrefixes: string[]:

externalLinkPrefixes:
  - /site-a/
  - /site-b/

And then handle these link prefixes at

rspress/packages/theme-default/src/layout/DocLayout/docComponents/link.tsx

Line 19 in 5309967

href={normalizeLinkHref(href)}