fix: do not expose empty cipassword to API

[jay7x]

Fixes Telmate/terraform-provider-proxmox#1097

[Tinyblargon]

@jay7x thank you for your contribution, could you add a test case to cement this behavior.

This is the test I'm referring to:

proxmox-api-go/proxmox/config_qemu_test.go

Line 16 in 032717b

func Test_ConfigQemu_mapToAPI(t *testing.T) {

Can you add the test case in the following category:

proxmox-api-go/proxmox/config_qemu_test.go

Line 431 in 032717b

{category: `CloudInit`, // Create CloudInit no need for update as update and create behave the same. will be changed in the future

Looking at it it's probably only a create case. If you want me to add the test case that's also possible.

[jay7x]

I'll try to add it this weekend :)