proposal: add the ability to define a range of codes in ExpectedStatuses

Now we can specify [ExpectedStatuses](https://gateway.envoyproxy.io/docs/api/extension_types/#httpactivehealthchecker) which defines a list of HTTP response statuses considered healthy.
It might be more convenient to modify or expand the ability to define ranges of response statuses.
Example:
```
expectedStatuses:
- start: 200
end: 201
- start: 401
end: 498
```