Add Romania vehicle registration plates

### Description

Add Romanian vehicle Registration Plate Generator
https://en.wikipedia.org/wiki/Vehicle_registration_plates_of_Romania

### LINQPad Code Example

```
var fakeAuto = new Faker("ro")
.RuleFor(a => a.Plate, (f, _) => f.Vehicle..RoRegistrationPlate())

```

### What alternatives have you considered?

No

### Could you help with a pull-request?

Yes

Start with the LINQPad example and inspect the existing vehicle-provider entry points for the "ro" locale. Use the linked Romanian registration-plate reference to define RoRegistrationPlate, then verify that Faker("ro") can produce Romanian plates through the example.

Written by the indexing model from the issue text.