### 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_
from localstack import config
from localstack.aws.api.lambda_ import Runtime
from localstack.aws.api.s3 import StorageClass
from localstack.config import LEGACY_V2_S3_PROVIDER, S3_VIRTUAL_HOSTNAME
from localstack.constants import (
    AWS_REGION_US_EAST_1,
    LOCALHOST_HOSTNAME,
    SECONDARY_TEST_AWS_ACCESS_KEY_ID,
    SECONDARY_TEST_AWS_SECRET_ACCESS_KEY,
    TEST_AWS_ACCESS_KEY_ID,
)
from localstack.services.s3 import constants as s3_constants
from localstack.services.s3.utils import (
    RFC1123,
    etag_to_base_64_content_md5,
    parse_expiration_header,
    rfc_1123_datetime,
)
from localstack.testing.aws.util import is_aws_cloud
from localstack.testing.pytest import markers
from localstack.testing.snapshots.transformer_utility import TransformerUtility
from localstack.utils import testutil
from localstack.utils.aws.request_context import mock_aws_request_headers
from localstack.utils.aws.resources import create_s3_bucket
from localstack.utils.files import load_file
from localstack.utils.run import run
from localstack.utils.server import http2_server
from localstack.utils.strings import (
    checksum_crc32,
    checksum_crc32c,