Add kubernetes models for API server, and yaml generation

[cbgbt]

Issue number: #77

Description of changes:
This change adds a build step which converts our Rust models into YAML files which can be deployed to kubernetes.

Included is a client which can be used to create and update the BottlerocketNode custom resources

Testing done:
The YAML files were applied to an EKS cluster, and then a BottlerocketNodeClient was used to create a BottlerocketNode custom resource, and update its status:

$ kubectl describe brn
Name:         brn-ip-192-168-66-198.us-west-2.compute.internal
Namespace:    brupop-bottlerocket-aws
Labels:       <none>
Annotations:  <none>
API Version:  brupop.bottlerocket.aws/v1
Kind:         BottlerocketNode
Metadata:
  Creation Timestamp:  2021-10-05T19:41:03Z
  Generation:          1
  Managed Fields:
    API Version:  brupop.bottlerocket.aws/v1
    Fields Type:  FieldsV1
    fieldsV1:
      f:metadata:
        f:ownerReferences:
          .:
          k:{"uid":"623ca9b3-bfc6-4c0f-b5d8-d8bd320a0a2f"}:
            .:
            f:apiVersion:
            f:kind:
            f:name:
            f:uid:
      f:spec:
        .:
        f:state:
        f:version:
      f:status:
        .:
        f:available_versions:
        f:current_state:
        f:current_version:
    Manager:    unknown
    Operation:  Update
    Time:       2021-10-05T19:41:03Z
  Owner References:
    API Version:     v1
    Kind:            BottlerocketNode
    Name:            ip-192-168-66-198.us-west-2.compute.internal
    UID:             623ca9b3-bfc6-4c0f-b5d8-d8bd320a0a2f
  Resource Version:  36761
  UID:               0d69e179-dbda-4058-bf4f-8e099b517a52
Spec:
  State:    WaitingForUpdate
  Version:  <nil>
Status:
  available_versions:
    1.3.0
  current_state:    WaitingForUpdate
  current_version:  1.2.1
Events:             <none>

Terms of contribution:

By submitting this pull request, I agree that this contribution is dual-licensed under the terms of both the Apache License, version 2.0, and the MIT license.

[arnaldo2792]

👢

[gthao313]

available_versions might be an empty Vec which means current version is the latest version, I think it's better to use Option<Vec<String>>

[cbgbt]

I think it's only best to wrap a Vec in Option if there is a meaningful distinction between an empty vector, and a null one. In this case, both represent the absence of updates, so it's probably best to only allow a single representation of it if possible. I think not using Option is more clear here.