EF Core improvements

[joaopgrassi]

• Change how migrations work today (Data project will be just a class lib instead of a webapp) Change NuGetTrends.Data project type #77
• Introduce EntityTypeConfiguration for each entity, so the DbContext file is clear of configuration
• Use the package for camel case Postgres and remove our impl Drop custom EF schema snake_case code in favor of EFCore.NamingConventions #85
• Figure it out why we have a pending migration and try to "remove" it (there were no intentional model changes, but the enabling of null ref types + the new ef pkg versions introduced unwanted changes)

The migrations that show up now are due to:

• Npgsql now generates Identity columns instead of serial. https://www.npgsql.org/efcore/release-notes/3.0.html#default-value-generation-strategy-is-now-identity. We might want to bite the bullet and run this, most certanly in a backup

[dnfclas]

All CLA requirements met.

[bruno-garcia]

vai que da