Deploy mithril demo infra on 'preview' network

[abailly-iohk]

Why

Current infrastructure is deployed on testnet which is soon to be deprecated and is incompatible with newest developments on cardano-node (1.35.3-X series).

What

• Upgrade mithril-infra configuration to deploy over preprod network
• Upgrade cardano-node docker to 1.35.3-new

[SViksha]

also on PreView

[abailly-iohk]

@SViksha We'll do preview first and then preprod

[jpraynaud]

The Mithril Aggregator hosted on GCP now runs on the preview network and has produced its first snapshot 👍

To make a Mithril Signer work on this network, here is a list of mandatory tasks to complete:

1. Recompile the Mithril Signer node as explained in this guide
2. Use the NETWORK=preview environment variable to start the Mithril Signer node
3. Wait for 2 epochs before the Mithril Signer node starts producing Individual Signatures

⚠️ Currently, the Mithril Signer node must wait for ~2/3 hours before the REGISTERED state is achieved in the state machine. This is normal behavior and the wait delay will be reduced very shortly when #438 will be merged.