[Bug]: Http typekits are not exposed and documentation is missing info on how to use

### Describe the bug

I had to add

```typescript
import "@typespec/http/experimental/typekit";
```

To make them work in a non Alloy environment. Otherwise typescript doesn't see merged typekit declaration and missing all http typekits.

This should be either documented or exposed and working with http module import.

### Reproduction

```typescript
import { getHttpOperation } from "@typespec/http";
import { $ } from "@typespec/compiler/typekit";
// import "@typespec/http/experimental/typekit"; // uncomment to make this work

const [httpOperation] = getHttpOperation(program, operation);
$(program).httpOperation.flattenResponses(httpOperation);
```

### Checklist

- [x] Follow our [Code of Conduct](https://github.com/microsoft/typespec/blob/main/CODE_OF_CONDUCT.md)
- [x] Check that there isn't already an issue that request the same bug to avoid creating a duplicate.
- [x] Check that this is a concrete bug. For Q&A open a [GitHub Discussion](https://github.com/Microsoft/typespec/discussions).
- [x] The provided reproduction is a [minimal reproducible example](https://stackoverflow.com/help/minimal-reproducible-example) of the bug.