### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

We are using the `Authorization` header for routing purposes

```
 "authorization: AWS4-HMAC-SHA256 <...>"
```

https://github.com/localstack/localstack/issues/5770

### Expected Behavior

Use a custom header to avoid causing confusion with backend integrations

### How are you starting LocalStack?

With a `docker run` command

### Steps To Reproduce

Run a custom HTTP integration without authorisation

### Environment

```markdown
- OS: 
- LocalStack:
```


### Anything else?

No
"""Base class for region-specific backends for the different APIs.
    RegionBackend lookup methods are not thread safe."""
    REGIONS: Dict[str, T]
    name: str  
    @classmethod
    def get(cls: Type[T], region: str = None) -> T:
        region = region or cls.get_current_request_region()
        regions = cls.regions()
        backend = regions.get(region)
        if not backend:
            backend = cls()
            backend.name = region
            regions[region] = backend
        return regions[region]
    @classmethod
    def regions(cls: Type[T]) -> Dict[str, T]:
        if not hasattr(cls, "REGIONS"):
            
            cls.REGIONS = {}
        return cls.REGIONS
    @classmethod
    def get_current_request_region(cls):
        return aws_stack.get_region()
    @classmethod
    def reset(cls):
        """Reset the (in-memory) state of this service region backend."""
        
        cls.REGIONS = {}
        return cls.regions()
def append_cors_headers(request_headers=None, response=None):