`serviceName` hardcoded with `-headless` conflicts when `serviceHeadless.enabled` is `false`

[jcudit]

-headless is hardcoded here, which breaks routing via the non-headless service when service.enabled is true:

helm-charts/charts/vector/templates/statefulset.yaml

Line 30 in d64abd0

serviceName: {{ template "vector.fullname" . }}-headless

This relates to #267 as I'm disabling the headless service because the chart fails to apply with annotation-driven load balancer configuration.

A possible fix is to conditionally add the -headless suffix depending on the value of serviceHeadless.enabled.