affiliations: switch to datastreams

[tmorrell]

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Description

This PR upgrades affiliation to a datastream and makes it consistent with funders and ROR v2 #318.

inveniosoftware/invenio-app-rdm#2680 is needed for it to work within RDM

Checklist

Ticks in all boxes and 🟢 on all GitHub actions status checks are required to merge:

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• I've created logical separate commits and followed the commit message format.
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Frontend

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