### 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_
s3_client.get_(Bucket=s3_bucket, Key="/bar")
        response = s3_client.get_(Bucket=s3_bucket, Key="/foo")
        assert response["Body"].read() == b"foobar"
        response = s3_client.get_(Bucket=s3_bucket, Key="bar")
        assert response["Body"].read() == b"barfoo"
        response = s3_client.get_(Bucket=s3_bucket, Key="/bar/foo/")
        assert response["Body"].read() == b"test"
    @markers.aws.validated
    @markers.snapshot.skip_snapshot_verify(
        condition=is_v2_provider,
        paths=["$..ServerSideEncryption"],
    )
    def test_metadata_header_character_decoding(self, s3_bucket, snapshot, aws_client):
        snapshot.add_transformer(snapshot.transform.s3_api())
        # Ob
        # ht
        # put 
        _key = "key-with-metadata"
        metadata = {"TEST_META_1": "foo", "__meta_2": "bar"}
        aws_client.s3.put_(Bucket=s3_bucket, Key=_key, Metadata=metadata, Body="foo")
        metadata_saved = aws_client.s3.head_(Bucket=s3_bucket, Key=_key)
        snapshot.match("head-", metadata_saved)
        # no
        assert metadata_saved["Metadata"] == {"test_meta_1": "foo", "__meta_2": "bar"}
    @markers.aws.validated
    @markers.snapshot.skip_snapshot_verify(
        condition=is_v2_provider,
        paths=["$..ServerSideEncryption"],
    )
    def test_upload_file_multipart(self, s3_bucket, tmpdir, snapshot, aws_client):