Support for a default enum value?

@ardalis, I am wondering what your thoughts are regarding the idea of having the option of specifying a default enum value for a class inheriting from SmartEnum.

For example, let's say I have the following enum:
```cs
public class Status : SmartEnum
{
public static readonly Status Other = new(nameof(Pending), 0);
public static readonly Status Pending = new(nameof(Pending), 1);
public static readonly Status Completed = new(nameof(Completed), 2);

private Status(string name, int value) : base(name, value) { }
}
```
Then, if I were to do this:
```cs
var status = Status.FromName("Cancelled");
```
An exception gets thrown. Instead, I would prefer to have the `Other` status returned if an unknown is specified in the `FromName` method. How would you recommend solving this? Would there be any benefit to adding a new constructor to `SmartEnum` that allows an enum to specify whether it is to be used as a default value?

Start by reviewing the SmartEnum FromName API and its current exception behavior. Define how a derived enum designates a fallback such as Other, then specify and test the behavior for unknown names while preserving existing known-name lookups.

Written by the indexing model from the issue text.