[RFC] Add Sailthru iOS SDK

[Ash Furrow]

New Dependency

Name: SailthruMobile iOS SDK

URL: https://github.com/carnivalmobile/carnival-ios-sdk

Motivation

Artsy is integrating with Sailthru and we need to integrate their SDK into our app. I decided on the Objective-C SDK (in lieu of the React Native one) because all our analytics code still runs through the Objective-C part of our app. See the ticket and the product brief 🔐 for more context.

This isn't an open source dependency, as Sailthru's SDK is a compiled framework. But in the spirit of taking ownership of all the code we ship, including our dependencies, I'm following our guidelines. This is less of a Request For Comments and more of an Architecture Decision Record.

Check List

• Have you read over the source code?
• Has had a release in the last year, or looks done and stable?
• Could you fit this codebase in your head after reading the source?
• Is this the stand-out obvious answer to a particular domain problem?
• Do you expect your team to be the only people who know about this dependency?
• Is this obviously being used in production by the maintainers? Is it battle-tested?
• Does our bundle already include a (transitive) dependency that solves the problem and could we use that
  instead?
• Do you feel well versed in the domain of this dependency and/or could you maintain it if that needs to become
  an option?

Alternatives

None. We have to adopt their SDK in order to use their service.