Add missing attributes to /system/function/{functionName}

Expected Behaviour

Attributes used to create a function with the POST endpoint should be mirrored when retrieving the function meta data using the GET endpoint

Current Behaviour

The attributes are currently as follows:

Possible Solution

1. swagger.yml add missing attributes to FunctionListEntry
2. gateway/requests/requests.go add missing attributes to Function type
3. faas-swarm/handlers/reader.go add missing attributes in readServices func
4. faas-netes add missing attributes
5. faas-operator add missing attributes
6. faas-cli describe verb when merged may need updating

Context

I'm writing a terraform provider for openfaas, to work well with terraform, it's best if the underlying infrastructure apis have mirrored POST/GET endpoints. This is also a very common practice in REST apis

Start with swagger.yml's FunctionListEntry and gateway/requests/requests.go's Function type, then trace readServices in faas-swarm/handlers/reader.go. Check the corresponding faas-netes and faas-operator implementations and the faas-cli describe verb. Done means the GET function metadata mirrors the POST attributes, with the sensitive registryAuth decision resolved.