### 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
ACL_EXPOSE_HEADERS,
    ACL_METHODS,
    ACL_ORIGIN,
    ACL_REQUEST_HEADERS,
)
from requests.models import Request, Response
from werkzeug.exceptions import HTTPException
from localstack import config
from localstack.config import (
    EXTRA_CORS_ALLOWED_HEADERS,
    EXTRA_CORS_ALLOWED_ORIGINS,
    EXTRA_CORS_EXPOSE_HEADERS,
)
from localstack.constants import (
    APPLICATION_JSON,
    AWS_REGION_US_EAST_1,
    BIND_HOST,
    HEADER_LOCALSTACK_REQUEST_URL,
)
from localstack.services.messages import Headers, MessagePayload
from localstack.services.messages import Request as RoutingRequest
from localstack.services.messages import Response as RoutingResponse
from localstack.utils.aws import aws_stack
from localstack.utils.aws.aws_responses import LambdaResponse
from localstack.utils.aws.aws_stack import is_internal_call_context
from localstack.utils.aws.request_context import RequestContextManager, get_proxy_request_for_thread
from localstack.utils.crypto import generate_ssl_cert
from localstack.utils.functions import empty_context_manager
from localstack.utils.json import json_safe
from localstack.utils.net import wait_for_port_open