iOS end to end workflow changes related to iOS 17 and iPad

[niklasberglund]

This PR changes how iOS end to end test workflows are set up because we ran into some issues. The test iPhone was changed. First it was changed to an iPad and then to another iPhone. The new iPhone is running iOS 17 which don't reinstall the app when launched from tests. So the workflow instead invoke multiple test jobs which run one test suite each. This way we have more control of what we want to do in between test suite runs in CI(uninstall app).

This PR also adds support for running tests on iPad, some minor changes were needed. There's a new configuration property TEST_DEVICE_IS_IPAD which should be set in UITests.xcconfig. Also it can now be configured in UITests.xcconfig whether app should be uninstalled in test suite teardown. This is by default true(1) for running locally, set to false(0) in CI.

The workflow file ios-end-to-end-tests.yml is now a reusable workflow which is reused by other thin workflows.

More information about this in ios/MullvadVPNUITests/README.md.

There are some things that should probably still be improved on:

• Test device is currently specified by setting the environment variable TEST_DEVICE_UDID in ios-end-to-end-tests.yml and ios-end-to-end-tests-settings-migration.yml. This should be more dynamic to be easier to set up runner on other computers and to run tests on multiple devices.
• Settings migration tests have not been updated. They might be easier to maintain if they also use the reusable workflow.

The changes in this PR can be tested by running the iOS end-to-end tests workflow https://github.com/mullvad/mullvadvpn-app/actions/workflows/ios-end-to-end-tests.yml and specifying the PR branch. The PR also introduces other workflows but unfortunately they won't show up in GitHub until they've been merged to main. It might be easiest to ask Niklas for a demo?

The ios/MullvadVPNUITests/README.md has been updated to reflect changes introduced in this PR and better describe the end to end tests, but all README changes are in a separate PR #6446

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This change is 

[pinkisemils]

Reviewed 14 of 15 files at r1, 2 of 2 files at r6, all commit messages.
Reviewable status: all files reviewed, 3 unresolved discussions (waiting on @niklasberglund)

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.github/workflows/ios.yml line 59 at r6 (raw file):

        with:
          limit-access-to-actor: true
          detached: true

I don't think we need this in prod.

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ios/MullvadVPNUITests/README.md line 51 at r6 (raw file):

* `MullvadVPNUITestsVerifyDNSSettingsChanged` - Verify custom DNS settings still changed
* `MullvadVPNUITestsChangeSettings` - Change all settings except custom DNS setting
* `MullvadVPNUITestsVerifySettingsChanged` - Verify all settings except custom DNS setting still changed

I need that trailing newline.

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ios/MullvadVPNUITests/tests.json line 18 at r6 (raw file):

        ]
    }
}

This could also do with a newline at the end.

[buggmagnet]

Reviewed 1 of 15 files at r1.
Reviewable status: 14 of 16 files reviewed, 3 unresolved discussions (waiting on @niklasberglund and @pinkisemils)

[mojganii]

Reviewable status: 1 of 16 files reviewed, 3 unresolved discussions (waiting on @buggmagnet, @niklasberglund, and @pinkisemils)

Reviewer is on vacation