Move persistence into separate Microsoft.Orleans.Persistence package

I propose that we move grain persistence into a package separate from the core of Orleans

This helps to keep the core of Orleans as focused as possible and also improves the ability for us to evolve persistence APIs

Related to #7410, which proposes the same for reminders

The issue names no files, tests, or entry points. Start by reviewing the Orleans repository structure and related issue #7410 to identify the grain-persistence code and package boundaries. Done means persistence is moved into a separate Microsoft.Orleans.Persistence package while the core remains focused and the persistence APIs can evolve independently.

Written by the indexing model from the issue text.