Create lib for wrapping Nebraska's REST API

[joaquimrocha]

Current situation

We have a REST API but we should make it more accessible for go users, so we can more easily automate common workflows.

Impact

It'll make it easier to manipulate Nebraska and improve a lot of what can be automated.

**Implementation options

Here is a rough idea of what it should look like:

Each Nebraska server should have an endpoint for its nebraska related functions: SERVER_BASE_URL/v1/nebraska

We have 5 main actors (or 4 main actors under each application):

• Application
  • Group
  • Channel
  • Package
  • Instance

There's a Nebraska struct whose functions are related to the applications, and to hold the SERVER_URL: ListApps() []Application, err GetApp(id_or_product_id string) Application, err DeleteApp(id_or_product_id string) err AddApp(app Application) err -> See Add(ACTOR) below for some text on the reasoning.

Then, since the rest of the actors are really related to an application, the Application struct will have: Groups() []Group Channels() []Channel Packages() []Package Instances() []Instance DeleteACTOR(id string) err GetACTOR(id string) ACTOR, err Update(item ACTOR) err Add(item ACTOR) ACTOR, err -> Will take an ACTOR instance and try to add it to the database. I thought about having maybe an ACTORConfig, for a NewACTOR func but maybe we can go with just creating an instance and adding it like this. It returns a complete actor on success, i.e. with the ID it will get from the DB, etc.

Functions for the Application struct which will list the actors belonging to this app:

Functions for the Group struct: its fields, including Channel for getting the channel, and Instances() []Instance

Functions for the Channel struct: its fields, including Package for getting the package

For the Package and Instance structs: only their fields

Rough example for assigning a new channel to all the groups in an app:

import (
  nebraska "github.com/kinvolk/nebraska/v1"
)

SERVER_URL := "https://myserver.com/v1/nebraska"

n := nebraska.New(SERVER_URL)

app, err := n.GetApp("io.kinvolk.Headlamp")
...

channel, err := app.Add(nebraska.Channel{Name: "stable"})
...

groups, err := app.GetGroups()
...
for _, group := range groups {
  group.Channel = channel
  app.Update(group)
}