### 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
try:
            partition = self._get_partition_for_region(region)
        except ArnPartitionRewriteListener.InvalidRegionException:
            try:
                
                
                partition = self._get_partition_for_region(config.DEFAULT_REGION)
            except self.InvalidRegionException:
                
                partition = self._get_partition_for_region(AWS_REGION_US_EAST_1)
        return partition
    def _get_partition_for_region(self, region: str) -> str:
        
        
        if region.startswith("us-gov-"):
            return "aws-us-gov"
        elif region.startswith("us-iso-"):
            return "aws-iso"
        elif region.startswith("us-isob-"):
            return "aws-iso-b"
        elif region.startswith("cn-"):
            return "aws-cn"
        elif re.match(r"^(us|eu|ap|sa|ca|me|af)-\w+-\d+$", region):
            return "aws"
        else:
            raise ArnPartitionRewriteListener.InvalidRegionException(
                f"Region ({region}) could not be matched to a partition."
            )
T = TypeVar("T", bound="RegionBackend")
class RegionBackend(object):