Respect allow send as guest configuration in resolver

[pmclain]

Description (*)

Resolver throws GraphQlAuthorizationException when sending as guest if allow
send as guest is disabled.

Fixed Issues (if relevant)

1. Guest User can SendFriend products ignoring restrictions #732

Manual testing scenarios (*)

Send a Friend Mutation:

mutation {
  sendEmailToFriend(
    input: {
      product_id: {$productId}
      sender: {
        name: "Name"
        email: "[email protected]"
        message: "Lorem Ipsum"
      }          
      recipients: [{
        name: "Recipient Name 1"
        email:"[email protected]"
      }]
    }
  ) {
    sender {
      name
      email
      message
    }
    recipients {
      name
      email
    }
  }
}

1. Vanilla Magento install. Default value for Stores > Configuration > Catalog > Email a Friend > Allow For Guests is No
2. Execute above mutation as guest.
3. Validate GraphQlAuthorizationException
4. Authenticate as customer
5. Execute mutation including authentication token
6. Validate success response
7. Set Allow for Guests to Yes
8. Repeat items 2-6. Guest mutation should no longer return GraphQlAuthorizationException

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds are green)

[ghost]

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