Update Integrations to include Nylas Email API code sample

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Goals

1. Update Integrations section to include Nylas Email API
2. Share steps and code sample for using Nylas Email API to send emails

Background

I’ve already done most of the work and created similar content in the past on how to create React email templates and send them using Nylas. I like to add this to the React.email site for developers to discover as an integration option.

Proposal

Yes, I will complete the integration code sample + documentation end-to-end :)