allow to pin IPs of vault services

**Is your feature request related to a problem? Please describe.**
We want the vault services to have fixed IPs (to allow for IP-based rules).

**Describe the solution you'd like**
Extend the helm templates to add a `loadBalancerIP`

``` yaml
# helm/templates/server-ha-active-service.yaml
# ...
spec:
{{- if .Values.server.service.type}}
type: {{ .Values.server.service.type }}
# pin IP
{{- if not (empty .Values.server.ha.activeIP) }}
loadBalancerIP: {{ .Values.server.ha.activeIP }}
{{- end}}
# ...

# helm/templates/server-ha-standby-service.yaml
# ...
spec:
{{- if .Values.server.service.type}}
type: {{ .Values.server.service.type }}
# pin IP
{{- if not (empty .Values.server.ha.standbyIP) }}
loadBalancerIP: {{ .Values.server.ha.standbyIP }}
{{- end}}
# ...

# helm/templates/server-service.yaml
# ...
spec:
{{- if .Values.server.service.clusterIP }}
clusterIP: {{ .Values.server.service.clusterIP }}
{{- else if eq .Values.server.service.type "LoadBalancer" }}
type: {{ .Values.server.service.type }}
# pin IP
{{- if not (empty .Values.server.service.loadBalancerIP) }}
loadBalancerIP: {{ default "" .Values.server.service.loadBalancerIP }}
{{- end }}
# ...
```

**Describe alternatives you've considered**
-

**Explain any additional use-cases**
-

**Additional context**
if this is a feature regarded as beneficial i'd implement it.