Allow users to create a stack for managing pkg applications

[jsteenb2]

We want to introduce the concept of a stack, which is a container for which to apply packages that maintain state of their application.

A stack record will look like the following:

{
  "stack_id": "UUID",
  "created_at": "TIME STAMP",
  "updated_at": "TIME STAMP",
  "config": {
    "urls": ["URL_TO_ORG_PKG", "URL_TO_SHARED_K8s_PKG"]
  },
  "resources": [
    {
      "apiVersion": "v2alpha1",
      "kind": "Bucket",
      "name": "bucket_1",
      "id": "UUID"
    },
    {
      "apiVersion": "v2alpha1",
      "kind": "Label",
      "name": "label_1",
      "id": "UUID"
    },
    {
      "apiVersion": "v2alpha1",
      "kind": "Dashboard",
      "name": "dash_1",
      "id": "UUID"
    },
    {
      "apiVersion": "v2alpha1",
      "kind": "Dashboard",
      "name": "dash_2",
      "id": "UUID"
    },
    {
      "apiVersion": "v2alpha1",
      "kind": "Task",
      "name": "task_1",
      "id": "UUID"
    }
   ...
  ]
}

The stack record consists of all resources that exist as a result of running the pkg. This issue is to create the foundation for which pkger will use this stack to manage state of its application of a pkg.

A new API endpoint is required

POST /api/v2/packages/stack

with the following req body (optional):

{
   urls: ["URL_TO_PKG_1", "URL_TO_PKG_2", ...]
}

with the following resp body:

{
   "stackID":  "UUID",
   "createdAt": "TIMESTAMP",
   "updatedAt": "TIMESTAMP",
   "config": {
      urls: [...valid urls or empty collection]
   }
}

AC

• new endpoint POST /api/v2/packages/stack to initialize the stack
  • involves a lot of plumbing
• stack record includes the following when created:

{
"stack_id": "UUID",
  "created_at": "TIME STAMP",
  "updated_at": "TIME STAMP",
  "config": {
    // if provided
    "urls": ["URL_TO_ORG_PKG"] 
  },
  "resources": []
}