feat(openapi-v3): responses decorator

[virkt25]

connected to #1531

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This PR:

• Ensures we set a default responses property on a Controller methods OpenAPI Spec if one isn't given
• Extends the OpenAPI spec by introducing a x-ts-type property that can be used to specify the schema of a response object. Can also be used to specify the type of array items.

content: {'x-ts-type': Todo} => content: {schema: {$ref: '#components/schemas/Todo'}}
content: {schema: {type: 'array', items: {x-ts-type: Todo}}} => content: {schema: {type: 'array', items: {$ref: '#components/schemas/Todo'}}}

• Refactors generate-schema to have a single function to resolve schema from a Function.
• Updates CLI Controller template to set a responses object based on the Model
• Updates example-todo / example-todo-list to set responses object

This PR introduces:
- a new @responses decorator that can be used to decorate a Controller method with the appropriate OpenAPI responses object.
- for controller's not decorated with this property, or via the @operation and family (get, post, etc.) of decorators, we generate a default responses object to be OpenAPI 3.0 compliant
- controller-spec generator can set Model as $ref for {schema: Model} or {schema: {type: 'array', items: Model}}}in the responses object.~ ~- Decorateexample-todowith@Responses()` decorator as an example. Once this PR is agreed upon, a follow up PR/commit will add decoration to CLI template + remaining examples + docs

Checklist

• npm test passes on your machine
• New tests added or existing tests modified to cover all changes
• Code conforms with the style guide
• API Documentation in code was updated
• Documentation in /docs/site was updated
• Affected artifact templates in packages/cli were updated
• Affected example projects in examples/* were updated