### 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_
acp = {
            "Owner": owner,
            "Grants": [
                {
                    "Grantee": {"ID": owner["ID"], "Type": "CanonicalUser"},
                    "Permission": "FULL_CONTROL",
                },
                {
                    "Grantee": {
                        "URI": "http://acs.amazonaws.com/groups/s3/LogDelivery",
                        "Type": "Group",
                    },
                    "Permission": "WRITE",
                },
            ],
        }
        aws_client.s3.put_bucket_acl(Bucket=s3_bucket, AccessControlPolicy=acp)
        response = aws_client.s3.get_bucket_acl(Bucket=s3_bucket)
        snapshot.match("get-bucket-acp-acl", response)
    @markers.aws.validated
    def test_s3_bucket_acl_exceptions(self, s3_bucket, snapshot, aws_client):
        list_bucket_output = aws_client.s3.list_buckets()
        owner = list_bucket_output["Owner"]
        with pytest.raises(ClientError) as e:
            aws_client.s3.put_bucket_acl(Bucket=s3_bucket, ACL="fake-acl")
        snapshot.match("put-bucket-canned-acl", e.value.response)
        with pytest.raises(ClientError) as e:
            aws_client.s3.put_bucket_acl(
                Bucket=s3_bucket, GrantWrite='uri="http://acs.amazonaws.com/groups/s3/FakeGroup"'
            )