Automatic merge from submit-queue.
Allow additional SGs to be added to API loadbalancer
Allow adding precreated additional security groups to the API loadbalancer using cluster spec:
```yaml
spec:
api:
loadBalancer:
type: Public
additionalSecurityGroups:
- sg-exampleid3
- sg-exampleid4
```
- [x] Adding additionalSecurityGroups cluster spec
- [x] Adding validation for repeated security groups
- [x] Adding validation for API loadbalancer security groups
- [x] Integration test for API loadbalancer and its security groups
- [x] Update API docs and cluster.spec docs