### 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_
snapshot.add_transformer(snapshot.transform.s3_api())
        bucket_name = s3_bucket
        for i in range(0, 10, 1):
            body = "test-" + str(i)
            key = "test-key-" + str(i)
            aws_client.s3.put_(Bucket=bucket_name, Key=key, Body=body)
        resp = aws_client.s3.list_s(Bucket=bucket_name, MaxKeys=100)
        snapshot.match("list-s", resp)
        assert 10 == len(resp["Contents"])
        s3_empty_bucket(bucket_name)
        aws_client.s3.delete_bucket(Bucket=bucket_name)
        resp = aws_client.s3.list_buckets()
        
        snapshot.match("list-buckets", resp)
        assert bucket_name not in [b["Name"] for b in resp["Buckets"]]
    @markers.aws.validated
    @markers.snapshot.skip_snapshot_verify(
        condition=is_v2_provider,
        paths=["$..ServerSideEncryption"],
    )
    def test_put_and_get__with_utf8_key(self, s3_bucket, snapshot, aws_client):