Handling of RFC7540 8.1.2.5 specification

Hi Team,

I would like pingora to follow the [RFC7540 8.1.2.5](https://datatracker.ietf.org/doc/html/rfc7540#section-8.1.2.5) specification or at least a feature that would allow switching between the old and new specification.

This has become a problem, because a website I'm working on can't handle the old way of parsing cookie headers
```
// old way
cookie: a=b
cookie: c=d
cookie: e=f
```

```
// new way
cookie: a=b; c=d; e=f
```

The issue lies in the [h2](https://github.com/hyperium/h2) crate. I have [mentioned this to the maintainers](https://github.com/hyperium/h2/issues/699) but they have decided that
> The place to implement that is in systems that do provide such things, such as Pingora

Hence why I'm requesting this feature