Uploaded result should be signed by the retriever

[xinaxu]

Tasks

Preview Give feedback

1. Every RG member needs to publish a public key to verify signature
2. Design and implement signing the result
3. Every RG member needs to deploy new RB with signature
4. Signature verification
5. Potentially backfilling unsigned test results
6. Open question : private key leak and rotation of private keys
7. Aggregation to repdao should be based on signature rather than based on retriever location