Feature: Migrate Trillian v1 Log to Tessera

[mhutchinson]

There are a number of existing logs in the world based on Trillian v1. This issue is to track the desire from the community to migrate any of these logs over to Tessera.

It's unlikely that we will create a useful standalone tool to perform this migration. There aren't that many logs that could be migrated, and each of these is likely to want specific features, or bespoke customization. e.g. Tessera doesn't support ExtraData, so any migration of a log with ExtraData would need to write this to something like a CAS alongside the Tessera instance.

That said, there's almost certainly stuff we can provide to help with this, if there is sufficient demand.