dnsdist: Add UUIDs to rules

dnsdist: Add UUIDs to rules

Having UUID assigned to rules makes it possible to track a given rule,
as opposed to the existing rule numbers that changed everytime a rule
was deleted or moved around. A rule now keeps the same UUID for the
lifetime of the dnsdist process and can even keep this UUID persistent
across restart if the UUID is provided when the rule is added:

```
addAction(AllRule(), AllowAction(), {uuid="123e4567-e89b-12d3-a456-426655440000"})
```

This is especially useful if the rules are managed via a central
controller using the console, or to display metrics retrieved via
the API.