Implement Rename of PortalJS to DataHub (PortalJS)

[rufuspollock]

We have renamed PortalJS to DataHub PortalJS and portaljs to datahub for the repo name.

We now need to make sure we update all the docs and make other changes ...

Docs etc

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1. Fixup repo links in examples and docs b/c otherwise they don't work - see e.g. Portaljs -> datahub github redirect does not work in create-next-app #1118 ✅2024-06-09 FIXED. Did some work in public datahub repo to correct all links
2. Migrate site content out of portaljs /site/ folder and move actual content to just be docs ...
3. Update datahub.io/docs page - will this just run off github.com/datopian/datahub/docs ??
4. BONUS: Refactor docs in general a bit (cloud vs opensource)

Redirects

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1. portaljs.org/ => datahub.io/opensource
2. portaljs.org/* => datahubio/docs/??
3. portaljs.com (only one page) => datahub.io/enterprise
4. next.datahub.io => datahub.io (not really used but now defunct)