Migrate end-to-end tests to staging environment and fix related issues

[niklasberglund]

In this branch the tests are running against staging production instead of production. The following Linear tickets have been addressed:

• Create client for partner API and use partner API for adding time to temporary accounts(https://linear.app/mullvad/issue/IOS-611/create-a-client-for-partner-api)
• Store test artifacts on GitHub to ease debugging(https://linear.app/mullvad/issue/IOS-614/store-test-artifacts-on-github)
• Store logs from debug builds as artifacts(https://linear.app/mullvad/issue/IOS-623/store-logs-from-debug-builds)
• Generate new temporary accounts for tests instead of using persistent accounts which might expire or have too many devices(https://linear.app/mullvad/issue/IOS-613/add-ability-to-generate-an-account-per-test)
• Run end to end tests in staging environment(https://linear.app/mullvad/issue/IOS-612/run-end-to-end-tests-in-staging-environment)
• Retry login when failing(https://linear.app/mullvad/issue/IOS-622/attempt-login-three-times-before-failing-test)

When running tests against staging instead of production there was some unexpected issues which has been addressed too, such as timing issues caused by staging responding faster than production and differences in number location and relay availability.

Regressions in main has also been adressed in this PR, and an input parameter was added for when the workflow is manually triggered. You can now optionally specify a test case/suite to run. The format must be MullvadVPNUITests/test-suite-name/test-case-name for example MullvadVPNUITests/RelayTests/testAppConnection to run testAppConnection or MullvadVPNUITests/RelayTests to run all test cases under the suite RelayTests.

To try out the changes in this PR you might want to run all end to end tests. Do so either by triggering the workflow and specifying branch create-a-client-for-partner-api-ios-611 https://github.com/mullvad/mullvadvpn-app/actions/workflows/ios-end-to-end-tests.yml or by running them all locally from Xcode.

If running the tests locally you must first make sure your UITests.xcconfig has the two new configuration properties introduced:

// URL for Mullvad provided JSON data with information about the connection. https://am.i.mullvad.net/json for production, https://am.i.stagemole.eu/json for staging.
AM_I_JSON_URL = https:/${}/am.i.stagemole.eu/json

// Specify whether app logs should be extracted and attached to test report for failing tests
ATTACH_APP_LOGS_ON_FAILURE = 0

⚠️ Note that there's a backend bug causing connecting to relay to sometimes fail when doing so immediately after creating an account and adding time to it using partner API ⚠️

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This change is 

[linear]

IOS-611 Create a client for partner API