rate limiting handling on marketing campaigns

[techgaun]

seems like sendgrid has a rate limit in place

Can we handle the rate limiting for marketing campaigns so we don't get errors instead?

Example error:

# result from api call: %{"errors" => [%{"field" => nil, "message" => "too many requests"}]}
** (MatchError) no match of right hand side value: nil
    (sendgrid) lib/sendgrid/marketing_campaigns/contacts/recipients.ex:39: SendGrid.Contacts.Recipients.handle_recipient_result/1