[chore] Move remark-wiki-link out to its own repo

[rufuspollock]

Move https://github.com/datopian/portaljs/tree/main/packages/remark-wiki-link back into its own repo: https://github.com/datopian/remark-wiki-link-plus

Why: this remark plugin is something people will want to use independently of flowershow/portaljs (see eg. landakram/remark-wiki-link#21). Having it "buried" in the packages here makes it harder to reuse, contribute to or star ...

Tasks

• Move https://github.com/flowershow/remark-wiki-link-plus to https://github.com/datopian/remark-wiki-link-plus
• Unarchive
• Move code out of here back into that repo
• ?? keep using @portaljs/remark-wiki-link or going back to remark-wiki-link-plus npm name??