Add support for Azure Sql Elastic Pool

### 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.

_No response_

### Describe the solution you'd like

When creating an Azure SqlServer resource it would be helpful to be able to define one or more elastic pools that databases may be added to rather than adding them directly to the SqlServer:

```cs
var sqlServer = builder.AddAzureSqlServer("sqlServer");
var pool = sqlServer.AddElasticPool("sqlPool");

// Added directly to the SqlServer
var db0 = sqlServer.AddDatabase("db0");

// Added to the Elastic Pool
var db1 = pool.AddDatabase("db1");
var db2 = pool.AddDatabase("db2");
```

### Additional context

_No response_