add grantless operations

[gberzins]

This pr checks whether request is being made to an endpoint which requires grantless access token.
Endpoints gathered from- https://developer-docs.amazon.com/sp-api/docs/grantless-operations

Relevant issues: https://github.com/ericcj/amz_sp_api/issues/38 https://github.com/ericcj/amz_sp_api/issues/3

Tested with notification endpoints. Code is not affecting any of generated code parts, so that shouldn't be an issue.

[gberzins]

@ericcj pinging you in case you didn't get notification and are interested!

[gberzins]

@ericcj will do sometime in upcoming week!