### 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
import os
import localstack_client.config
import localstack
VERSION = localstack.__version__
REGION_LOCAL = "local"
ENV_DEV = "dev"
HEADER_LOCALSTACK_EDGE_URL = "x-localstack-edge"
HEADER_LOCALSTACK_REQUEST_URL = "x-localstack-request-url"
HEADER_LOCALSTACK_TARGET = "x-localstack-target"
HEADER_AMZN_ERROR_TYPE = "X-Amzn-Errortype"
DEFAULT_PORT_EDGE = 4566
LOCALHOST = "localhost"
LOCALHOST_IP = "127.0.0.1"
LOCALHOST_HOSTNAME = "localhost.localstack.cloud"
LOCALSTACK_MAVEN_VERSION = "0.2.19"
DEFAULT_SERVICE_PORTS = localstack_client.config.get_service_ports()
BIND_HOST = "0.0.0.0"
if "TEST_AWS_ACCOUNT_ID" not in os.environ:
    os.environ["TEST_AWS_ACCOUNT_ID"] = "000000000000"
TEST_AWS_ACCOUNT_ID = os.environ["TEST_AWS_ACCOUNT_ID"]
MODULE_MAIN_PATH = os.path.dirname(os.path.realpath(__file__))
LOCALSTACK_ROOT_FOLDER = os.path.realpath(os.path.join(MODULE_MAIN_PATH, ".."))
INSTALL_DIR_INFRA = os.path.join(
    MODULE_MAIN_PATH, "infra"
)  
LOCALSTACK_VENV_FOLDER = os.environ.get("VIRTUAL_ENV")
if not LOCALSTACK_VENV_FOLDER: