Allow posting of proofs to finished proposals

[jeisses]

Feature

Enable posting of proofs to proposals that indicate that the author has finished the implementation.

Description

At the moment the final state of an accepted proposal is to be executed, which means the funding payment has been made by the DAO. There is no way to communicate on-chain that a proposal has been finished by the author.

Being able to proof finalizing a proposal on-chain is useful for several reasons:

• It signals to all DAO members that you are finished
• There is a proof of date/time and IPFS content hash of when you were finished
• It's an anchor point that can be later used for attesting delivery by the DAO (e.g. for payout on delivery)
• Proposal proofs indicate the track record of a member. Posting consistent and satisfying proofs should make it more easy to get your proposals voted in.

Steps

• Add post_proof action that accepts an IPFS hash
• Implement frontend in https://github.com/effectai/effect-dashboard
• Get approval for deployment with a proposal