[Valora] Reduce number of not needed requests to attestation services

[i1skn]

In celo-org/celo-monorepo#5925 we added support for 8 digit codes for verification. It introduces a 30% chance of asking the wrong validators for the full attestation code.

Improved solution

We fetch all the attestations (not only active) and take their id mod 10 instead of address of attestation issuer mod 10. In this case would only have a collision if user have more than 10 - completed attestations active attestations at the same time.

Reference: https://discord.com/channels/600834479145353243/732977310101405736/780918327072915456