[Epic] Retroactive funding + R21 and beyond

[idiom-bytes]

This is a macro ticket to track the work that needs to be delivered for R21 and beyond.

DoD:

• [ ] Retroactive Grants - Admin Portal oceandao-617
• [ ] Retroactive grants proposal ux workflow proposal-portal-200

DoD Ops:

• [ ] Retroactive grants workflow is communicated and operated manually via Airtable (https://github.com/oceanprotocol/oceandao/issues/616)
• [ ] Retroactive grants workflow is handled manually in the backend via mongo (TBD)
• [ ] Update proposals to adjust existing proposals & discretionary grants (https://github.com/oceanprotocol/oceandao/issues/526)