/api/v2/auth/login doesn't respond to OPTIONS (404) request for CORS check

## Gentics Mesh Version, operating system, or hardware.
- v1.4.0

## Operating System
- Kubernetes with Docker CRI

```
apiVersion: apps/v1
kind: Deployment
metadata:
name: cms
namespace: business
spec:
replicas: 1
selector:
matchLabels:
app: cms
template:
metadata:
labels:
app: cms
spec:
serviceAccountName: traefik-ingress-controller
containers:
- image: gentics/mesh:1.4.0
imagePullPolicy: Always
env:
- name: MESH_ELASTICSEARCH_URL
value: 'http://elasticsearch.business'
- name: MESH_ELASTICSEARCH_START_EMBEDDED
value: 'false'
- name: MESH_AUTH_KEYSTORE_PASS
value: 'h678fio876r57gikj76rf' - not the real one ;)
- name: MESH_MONITORING_HTTP_HOST
value: '0.0.0.0'
name: cms
ports:
- containerPort: 8080
volumeMounts:
- mountPath: /graphdb
name: cms-graphdb-volume
- mountPath: /keystore
name: cms-keystore-volume
- mountPath: /uploads
name: cms-uploads-volume
volumes:
- name: cms-graphdb-volume
persistentVolumeClaim:
claimName: cms-graphdb-pvc
- name: cms-keystore-volume
persistentVolumeClaim:
claimName: cms-keystore-pvc
- name: cms-uploads-volume
persistentVolumeClaim:
claimName: cms-uploads-pvc
---
---
apiVersion: v1
kind: Service
metadata:
name: cms-http-service
namespace: business
spec:
ports:
- port: 80
targetPort: 8080
protocol: TCP
name: http
selector:
app: cms
---
apiVersion: extensions/v1beta1
kind: Ingress
metadata:
annotations:
ingress.kubernetes.io/custom-response-headers: Access-Control-Allow-Origin:* || Access-Control-Allow-Methods:POST, GET, HEAD, OPTIONS, PUT, DELETE
name: cms-ingress
namespace: business
spec:
rules:
- host: cms.xxxxx.de
http:
paths:
- path: /
backend:
serviceName: cms-http-service
servicePort: 80
```

## JVM
- Official docker image tagged with 1.4.0

## Problem

When I try to log in via my angular frontend in order to obtain data via the graphql API I find the following log in my console:

`OPTIONS https://cms.xxxxx.de/api/v2/auth/login 404
Access to XMLHttpRequest at 'https://cms.xxxxx.de/api/v2/auth/login' from origin 'http://localhost:4200' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: It does not have HTTP ok status.`

When I try to reproduce it locally via curl it also returns the following 404 error:

```
curl -X OPTIONS https://cms.xxxxx.de/api/v2/auth/login -v
* Trying 37.24.225.83...
* ....
> OPTIONS /api/v2/auth/login HTTP/2
> Host: cms.xxxxxx.de
> User-Agent: curl/7.58.0
> Accept: */*
>
* Connection state changed (MAX_CONCURRENT_STREAMS updated)!
< **HTTP/2 404**
< access-control-allow-methods: POST, GET, HEAD, OPTIONS, PUT, DELETE
< access-control-allow-origin: *
< content-type: application/json; charset=utf-8
< vary: Accept-Encoding
< x-powered-by: getmesh.io
< content-length: 243
< date: Sat, 15 Feb 2020 23:42:48 GMT
<
{
"message" : "Not Found",
"internalMessage" : "The rest endpoint or resource for given path {/api/v2/auth/login} could not be found. Please verify that your Accept header is set correctly. I got {*/*}. It must accept {application/json}"
* Connection #0 to host cms.xxxxxx.de left intact
```

## Expected behaviour and actual behaviour

Expected: OPTIONS request to /v2/api/auth/login returns status code 200
Observed: OPTIONS request to /v2/api/auth/login returns status code 404 Not Found

Start by reproducing the OPTIONS request for /api/v2/auth/login and trace how the authentication API route handles preflight requests. Done means the endpoint returns HTTP 200 for OPTIONS and remains usable for the Angular client's CORS login flow; no source file or test is named in the issue.

Written by the indexing model from the issue text.