### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

- Localstack fails with HTTP 500, error code "InternalError", message "not enough values to unpack (expected 2, got 1)" when `CopySource` is an invalid string for `copy_object` API.

### Expected Behavior

- For the same API `copy_object`, the cloud fails with HTTP 400, error code "InvalidArgument".
- Localstack should handle invalid `CopySource` i.e., it is a dictionary with one value or an invalid string not adhering to "{bucket}/{key}" format.

### How are you starting LocalStack?

With a `docker run` command

### Steps To Reproduce

#### How are you starting localstack (e.g., `bin/localstack` command, arguments, or `docker-compose.yml`)

    docker run localstack/localstack

#### Client commands (e.g., AWS SDK code snippet, or sequence of "awslocal" commands)

    botoclient.copy_object(CopySource="Invalid_random_string", Bucket="test_bucket", Key=key) 


 test_bucket is a valid bucket.  

### Environment

```markdown
- OS: Ubuntu 22.04.2 LTS
- LocalStack: 2.1.0
- boto3: 1.28.6
```


### Anything else?

_No response_
"""
    Detects pre-signed URL from query string parameters
    Return True if any kind of presigned URL query string parameter is encountered
    :param context: the request context from the handler chain
    """
    
    query_parameters = context.request.args
    return any(p in query_parameters for p in SIGNATURE_V2_PARAMS) or any(
        p in query_parameters for p in SIGNATURE_V4_PARAMS
    )
def is_bucket_name_valid(bucket_name: str) -> bool:
    """
    ref. https://docs.aws.amazon.com/AmazonS3/latest/userguide/bucketnamingrules.html
    """
    return True if re.match(BUCKET_NAME_REGEX, bucket_name) else False
def get_permission_header_name(permission: Permission) -> str:
    return f"x-amz-grant-{permission.replace('_', '-').lower()}"
def get_permission_from_header(capitalized_field: str) -> Permission:
    headers_parts = [part.upper() for part in re.split(r"([A-Z][a-z]+)", capitalized_field) if part]
    return "_".join(headers_parts[1:])
def is_valid_canonical_id(canonical_id: str) -> bool:
    """
    Validate that the string is a hex string with 64 char
    """
    try:
        return int(canonical_id, 16) and len(canonical_id) == 64
    except ValueError:
        return False
def uses_host_addressing(headers: Dict[str, str]) -> str | None: