feat(oas): identify required fields in responses - store (#3282)

## Scope

Store routes

## What

Add OAS `required` to response schemas.

## Why

Code generator can use the `required` property of a schema to mark fields as optional or not when generating TS types.

## Test

* Run `yarn build`
* Run `yarn openapi:generate`
* Run `yarn redocly preview-docs docs/api/store/openapi.yaml --config=docs-util/redocly/config.yaml`
* Open the documentation preview URL in a browser (http://127.0.0.1:8080)
* Expect responses to have their fields declared as `required`

.changeset/short-plants-work.md

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+feat(oas): identify required fields in responses - store