Modifies domain objects after workshop

[ppkarwasz]

This PR modifies the schema of the domain objects according to the structure discussed in the Koala Workshop

[ppkarwasz]

This PR is based on #117.

[ppkarwasz]

Since there are lot of changes in this PR, here is a breakdown on how this integrates with the API Flow:

1. If a client knows the UUID of a TEA product, it can call /product/{uuid} to obtain such an object:
   

   transparency-exchange-api/spec/openapi.yaml

   Lines 174 to 192 in a805f3d

   	product:
   	type: object
   	description: A TEA product
   	properties:
   	uuid:
   	"$ref": "#/components/schemas/uuid"
   	name:
   	type: string
   	description: Product name
   	identifiers:
   	type: array
   	description: List of identifiers for the product
   	items:
   	"$ref": "#/components/schemas/identifier"
   	components:
   	type: array
   	description: List of TEA components for the product
   	items:
   	"$ref": "#/components/schemas/uuid"

2. If the client does not know the UUID of a TEA product, it can call /products with some query parameters and get a paginated list of the same objects as above.

3. Once the client has a list of UUIDs of TEA components, it probably should call /component/{uuid} to identify what those UUIDs correspond to. We probably can optimize the workflow by including the object below in the answer returned by /product/{uuid}:
   

   transparency-exchange-api/spec/openapi.yaml

   Lines 202 to 215 in 462b195

   	component:
   	type: object
   	description: A TEA component
   	properties:
   	uuid:
   	"$ref": "#/components/schemas/uuid"
   	name:
   	type: string
   	description: Component name
   	identifiers:
   	type: array
   	description: List of identifiers for the component
   	items:
   	"$ref": "#/components/schemas/identifier"

4. Once the client determines which component it is interested in it can call /component/{uuid}/versions with some query parameters (currently none) to list of the available versions of the component:
   

   transparency-exchange-api/spec/openapi.yaml

   Lines 226 to 248 in a805f3d

   	component-version:
   	type: object
   	description: A specific version of a TEA component
   	properties:
   	collection_uuid:
   	"$ref": "#/components/schemas/uuid"
   	version:
   	type: string
   	description: Version number of TEA component
   	identifiers:
   	type: array
   	description: List of identifiers for this component version
   	items:
   	"$ref": "#/components/schemas/identifier"
   	release_date:
   	"$ref": "#/components/schemas/date-time"
   	description: Release date
   	pre_release:
   	type: boolean
   	description: Marks if the version is a pre-release version
   	classifier:
   	type: object
   	description: Optional classifier to distinguish between artifacts

5. The last call is a call to /collection/{uuid}, which returns the latest version of the collection with a list of artifacts. Each artifact contains a list of artifact formats:
   

   transparency-exchange-api/spec/openapi.yaml

   Lines 259 to 275 in a805f3d

   	collection:
   	type: object
   	description: A collection of security-related documents
   	properties:
   	uuid:
   	"$ref": "#/components/schemas/uuid"
   	description: Must match the UUID of the corresponding `component_version` object
   	version:
   	type: integer
   	default: 1
   	description: Collection version, incremented each time its content changes.
   	update_reason:
   	"$ref": "#/components/schemas/collection-update-reason"
   	artifacts:
   	type: array
   	items:
   	"$ref": "#/components/schemas/artifact"