Add extensions methods for the MigrationBuilder

[GillesTourreau]

Creates a new package called PosInformatique.EntityFrameworkCore.Migrations to include the following extension methods:

public static OperationBuilder<SqlOperation> RenameForeignKey(this MigrationBuilder migrationBuilder, string name, string newName)
{
    return migrationBuilder.Sql($"EXECUTE sp_rename '{name}', '{newName}', 'OBJECT'");
}

public static OperationBuilder<SqlOperation> RenamePrimaryKey(this MigrationBuilder migrationBuilder, string name, string newName)
{
    return migrationBuilder.Sql($"EXECUTE sp_rename '{name}', '{newName}', 'OBJECT'");
}