chore: Instrument unit tests with CI Test Visibility 2.5.0

[ncreated]

What and why?

📦 This PR enables (back*) the Test Visibility instrumentation for our unit tests. With our tests being more stable in GitLab, we can leverage this instrumentation for more visibility into their performance and runs.

* we disabled Test Visibility a while ago, due to increased number of flaky test runs in Bitrise CI.

How?

Following the documentation, config ENVs are injected to every xcscheme and their values are exported in test.sh. Each scheme is configured to gather code coverage data, so we can later enable ITR.

🐶 This PR only integrates dd-sdk-swift-testing to an extra CI job meant for shadowing regular iOS unit tests runs. If we find our tests stable, we will integrate it to regular "Unit Test" jobs.

Unfortunately, there is no simpler way than applying the same configuration to all 14 schemes. The fact that we centralize tests execution through test.sh helps to control values, but the actual ENV injection must include forwarding it from Environment Variables list in xscheme definition. As explained in docs, the basic DD_TEST_RUNNER=1 ... xcodebuild test -scheme ... only works for Package.swift and not for Xcode project.

ENVs	configuration

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
• Add CHANGELOG entry for user facing changes

[datadog-datadog-prod-us1]

Datadog Report

Branch report: ncreated/chore/ci-visibility-shadow-build
Commit report: 5fa648b
Test service: dd-sdk-ios

✅ 0 Failed, 1848 Passed, 0 Skipped, 1m 15.14s Total Time

[ncreated]

blocking/ We also need to pass CI Provider variables to all tests.

[maxep]

Looks good 👍 Hope to remove the xcodeproj in a near future 🤞