[WIP] Entity Framework Core 7 Providers

[galvesribeiro]

This PR add Entity Framework 7 providers.

The goal is to provide the basic providers which are storage agnostic and rely only on Microsoft.EntityFrameworkCore like Microsoft.Orleans.XXXXX.EntityFrameworkCore.

We can provide database-specific packages like Microsoft.Orleans.XXXXX.EntityFrameworkCore.SqlServer, Microsoft.Orleans.XXXXX.EntityFrameworkCore.Postgresql, etc., which would depends on Microsoft.EntityFrameworkCore.SqlServer for example.

Also the developers can extend the underlying DbContext (i.e. add extra indexes, constraints, etc.) and/or provide custom migrations.

• [x] Clustering
• [x] Persistence
• [x] Reminders
• [x] Directory
• [x] Sql Server support
• [ ] MySql support
• [ ] PostgreSQL support

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