### 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
if isinstance(source, dict):
            result = {}
            for k, v in source.items():
                result[k] = self._adjust_partition(v, static_partition)
            return result
        if isinstance(source, list):
            result = []
            for v in source:
                result.append(self._adjust_partition(v, static_partition))
            return result
        elif isinstance(source, bytes):
            try:
                decoded = unquote(to_str(source))
                adjusted = self._adjust_partition(decoded, static_partition)
                return to_bytes(adjusted)
            except UnicodeDecodeError:
                
                return source
        elif not isinstance(source, str):
            
            return source
        return self.arn_regex.sub(lambda m: self._adjust_match(m, static_partition), source)
    def _adjust_match(self, match: Match, static_partition: str = None):
        region = match.group("Region")
        partition = self._partition_lookup(region) if static_partition is None else static_partition
        service = match.group("Service")
        account_id = match.group("AccountID")
        resource_path = match.group("ResourcePath")
        return f"arn:{partition}:{service}:{region}:{account_id}:{resource_path}"
    def _partition_lookup(self, region: str):