### 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
return validator["validateRequestBody"]
    @staticmethod
    def should_validate_request(validator):
        return validator.get("validateRequestParameters")
def run_authorizer(invocation_context: ApiInvocationContext, authorizer: Dict):
    
    pass
def authorize_invocation(invocation_context: ApiInvocationContext):
    client = aws_stack.connect_to_service("apigateway")
    authorizers = client.get_authorizers(restApiId=invocation_context.api_id, limit=100).get(
        "items", []
    )
    for authorizer in authorizers:
        run_authorizer(invocation_context, authorizer)
def validate_api_key(api_key: str, stage: str):
    usage_plan_ids = []
    client = aws_stack.connect_to_service("apigateway")
    usage_plans = client.get_usage_plans()
    for item in usage_plans.get("items", []):
        api_stages = item.get("apiStages", [])
        for api_stage in api_stages:
            if api_stage.get("stage") == stage:
                usage_plan_ids.append(item.get("id"))
    for usage_plan_id in usage_plan_ids:
        usage_plan_keys = client.get_usage_plan_keys(usagePlanId=usage_plan_id)
        for key in usage_plan_keys.get("items", []):
            if key.get("value") == api_key:
                return True
    return False
def is_api_key_valid(is_api_key_required: bool, headers: Dict[str, str], stage: str):