RUMM-346 Unify dependency manager tests

[ncreated]

What and why?

📦 This PR unifies Carthage, Cocoa Pods and SPM test projects.

How?

Now, all projects behave the same:

• cd <test-project> && make sources project to use current git branch;
• bitrise.yml runs unit tests and UI tests for each project and exports artifacts to Bitrise;
• testCallingLogicThatLoadsSDK() unit test calls basic SDK logic;
• testDisplayingUI() UI test launches the app and asserts that "Testing ..." label is visible;
• dedicated Build Phase runs linter;
• deployment target is set to iOS 13.0;
• Code Signing is configured for app target, unit test target and UI test target.

App Target
Every app target is just "Single View" app with default code + invocation of Datadog SDK.

UI Tests
Every test project has this basic UI and asserts the label is visible:

Unit Tests
Unit tests just invoke vc.viewDidLoad(), which guarantees that SDK is linked, loaded and run with no runtime error.

Code Signing
3 .xcconfigs are shared between all projects:

where datadog.xcodeproj is git-ignored as it might contain our secrets.

Review checklist

• Feature or bugfix MUST have appropriate tests (unit, integration)
• Make sure each commit and the PR mention the Issue number or JIRA reference

[buranmert]

ℹ️ let's merge #68 before this one

[buranmert]

only a couple of questions

[buranmert]

👍 👍 👍