Activate SNARK prover in `dev` network

[jpraynaud]

Why

We want to deploy a SNARK prover aggregator on the dev-follower-preview network which will allow us to test the creation of SNARK proof end to end.

What

Activate a SNARK prover on the dev-follower-preview network.

How

• Activate the Lagrange era on the dev-preview and dev-follower-preview networks to activate SNARK key registration
• Activate the Snark aggregate signature type on the dev-follower-preview network
• Make sure that SNARK proofs are created by the aggregator
• Make sure that the unstable client can verify a SNARK proof