* feat: add `hasPaywall` getter to `Offering`
Returns `true` if the offering has either a v1 or a v2 paywall
* docs: update some methods references changing `PaywallData` with "paywall", as `PaywallData` only refers to v1 paywalls
* docs: improve reference of `Offering`'s `paywall` and `paywallComponents` to mention the new `hasPaywall` property
* lint
* tests: add unit tests that check the `hasPaywall` property of `Offering`
* api tests: add `paywallComponents` and `hasPaywall` to SwiftAPITester
The new response is now represented by `GetIntroEligibilityResponse`, and has dedicated tests (`GetIntroEligibilityDecodingTests`) using a JSON fixture.
The operation becomes much simpler now, plus I've done a lot of code removing that was redundant.
The actual response handling is now 3 lines:
```swift
let result: [String: IntroEligibility] = Set(productIdentifiers)
.dictionaryWithValues { eligibilities?[$0] ?? .unknown }
.mapValues(IntroEligibility.init)
```
All the tests in `BackendGetIntroEligibilityTests` pass with no changes.
Antonio Pallares