Adapt the explorer to handle new aggregator `/artifact` routes

[jpraynaud]

Issue

Adapt the explorer to provide informations for the new artifact routes of the aggregator REST API:

• /snapshots and /snapshot/:id for the Cardano Full Immutable Files Snapshot
• /artifact/mithril-stake-distributions and /artifact/mithril-stake-distribution/:id for the Mithril Stake Distribution

Note

We will need to update the snapshot routes once they will be completely released to all the networks:

• /artifact/snapshots
• /artifact/snapshot/:id

Parent issue

#780