import: support enums in JSON schema

[eladb]

Respect enum in the JSON schema when importing CRDs and APIs.

For example, this schema:

"reclaimPolicy": {
    "description": "ReclaimPolicy specifies what will happen to this managed resource when its resource claim is deleted",
    "enum": [
        "Retain",
        "Delete"
    ],
    "type": "string"
}

Should be imported as:

interface Foo {
  readonly reclaimPolicy: ReclaimPolicy;
}

enum ReclaimPolicy {
  RETAIN = 'Retain',
  DELETE = 'Delete
}