### 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_
aws_client.s3.put__acl(
                Bucket=s3_bucket, Key=_key, GrantWrite='id="wrong-id"'
            )
        snapshot.match("put--grant-acl-wrong-id", e.value.response)
        acp = {
            "Grants": [
                {
                    "Grantee": {
                        "URI": "http://acs.amazonaws.com/groups/s3/LogDelivery",
                        "Type": "Group",
                    },
                    "Permission": "WRITE",
                }
            ]
        }
        with pytest.raises(ClientError) as e:
            aws_client.s3.put__acl(Bucket=s3_bucket, Key=_key, AccessControlPolicy=acp)
        snapshot.match("put--acp-acl-1", e.value.response)
        # add 
        acp["Owner"] = owner
        acp["Grants"][0]["Permission"] = "WRONG-PERMISSION"
        with pytest.raises(ClientError) as e:
            aws_client.s3.put__acl(Bucket=s3_bucket, Key=_key, AccessControlPolicy=acp)
        snapshot.match("put--acp-acl-2", e.value.response)
        # rest
        acp["Owner"] = {"ID": "wrong-id"}
        acp["Grants"][0]["Permission"] = "FULL_CONTROL"
        with pytest.raises(ClientError) as e:
            aws_client.s3.put__acl(Bucket=s3_bucket, Key=_key, AccessControlPolicy=acp)
        snapshot.match("put--acp-acl-3", e.value.response)