Set defaults on Sql server instances

### Is there an existing issue for this?

- [x] I have searched the existing issues

### Is your feature request related to a problem? Please describe the problem.

It would be good if possible to add defaults for AddAzureSqlServer that set the SKU to the minimum available version if nothing is specified.

The reason for this is that not specifying it leads to azure auto creating the database at a general purpose vcore 2 with an estimated monthly cost of ~400

### Describe the solution you'd like

```csharp
var sql = builder.AddAzureSqlServer("sqlserver").RunAsContainer(
container => container.WithLifetime(ContainerLifetime.Persistent)
).ConfigureInfrastructure(c =>
{
if (c.GetProvisionableResources().OfType().SingleOrDefault() is SqlDatabase db)
{
db.Sku = new SqlSku
{
Name = "Basic",
Tier = "Basic",
Capacity = 5
};
}
}).AddDatabase("sqldb", "DatabaseName");
```

### Additional context

Happy to complete this work