Support string name in service port: & allow service: name override

[cpboyd]

Fixes #43

• Support string name in service port: (from Support type string in ingress service port and pathType in ingress path #37, rebased to latest)
• Allow service: name override for individual services

Example below uses service: ssl-redirect with port: use-annotation.
In the current helm release, this doesn't work for two reasons:

1. service.servicename: helm supersedes the individual service names, even when they're specified.
2. No support for port.name & string port values.

service:
  servicename: helm

  ## Chartmuseum Ingress hostnames
  ## Must be provided if Ingress is enabled
  hosts:
    - name: helm.example.com
      path: /*
      service: helm

      ## Set this to true in order to enable TLS on the ingress record
      tls: false

  extraPaths:
    - path: /*
      service: ssl-redirect
      port: use-annotation