### 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_
GetObjectRequest,
    Grant,
    Grantee,
    HeadObjectRequest,
    InvalidArgument,
    InvalidRange,
    InvalidTag,
    LifecycleExpiration,
    LifecycleRule,
    LifecycleRules,
    Metadata,
    ObjectCannedACL,
    ObjectKey,
    ObjectSize,
    ObjectVersionId,
    Owner,
    Permission,
    PreconditionFailed,
    SSEKMSKeyId,
    TaggingHeader,
    TagSet,
)
from localstack.aws.api.s3 import Type as GranteeType
from localstack.aws.connect import connect_to
from localstack.services.s3.constants import (
    ALL_USERS_ACL_GRANTEE,
    AUTHENTICATED_USERS_ACL_GRANTEE,
    LOG_DELIVERY_ACL_GRANTEE,
    S3_CHUNK_SIZE,
    S3_VIRTUAL_HOST_FORWARDED_HEADER,