Check authentication Access Token with Store API

[leomp12]

Is your feature request related to a problem? Please describe.
Admin user should be able to fetch some private app routes from E-Com Plus dashboard without knowing operator token, by providing self authentication X-Access-Token.

Describe the solution you'd like
Check store_access_token param and check token and permissions from Store API:
https://github.com/ecomplus/application-starter/blob/master/functions/index.js#L44-L47

Describe alternatives you've considered
None yet.

Additional context
An example is to get subscribers list from https://github.com/ecomplus/app-offers-notification.