Introduce SnapshotInitializer

[Atralupus]

We have previously used the SnapshotInitializer. However, it is currently not functioning and does not handle LegacyAddress.

Since this initializer needs to be run whenever a new collection is created, it would be more sustainable and user-friendly to create a Mimir.SnapshotInitializer project and use it as a CLI tool.

The desired commands are as follows:

• download-snapshot (odin, heimdall)
• init (with collection name filter)

Handling LegacyAddress can be tricky, but it should be possible by first retrieving the avatar list from the snapshot and then iterating over the addresses based on the avatars.