iOS export configuration needs better validation

[Krumelur]

Godot version:
3.1 beta

OS/device including version:
macOS Mojave, Xcode

Issue description:
I've got a project that I'd like to export to iOS. The project can be found here: https://github.com/Krumelur/GodotTesting/tree/godot31_issue_24866
The export itself succeeds and I end up with an Xcode project file.
Deploying the project to a device fails with an error saying:

"App installation failed - No code signature found."

The reason is that no signing certificate is selected but cannot be selected. My assumption is that there is some Xcode project file compatibility issues. See video for details.

Steps to reproduce:

See videos for details. It will show exactly what I'm doing:

https://www.youtube.com/watch?v=5tXRo7uRPFE

• Open the project referenced above
• Export to iOS
• Try to deploy in Xcode

Minimal reproduction project:
see above

[ViktorEvil]

watched your video and downloaded your project. Managed to get it running on my iPhone by changing some of your export settings in Godot and let Xcode automatically sign the project

had to type in the text as shown in red (text was grey)

also had to change the Deployment target to iOS 10 to stop a flood of errors (had to do this on my project as well)

don't forget to add StoreKit.framework to your linked libraries as well or you will get a "linker command failed error" and the project will not build

[Krumelur]

Thanks. Yes, that fixed it. So let's get more concrete about the bug then that needs to be addressed:

• The fields "Code Sign Identity Debug/Release" should be compulsory, if possible dropdowns to pick the correct identity and have some hint about what the value is used for.
• The "Signature" requires some explanation. I just entered "I don't know what this is!" and it works. Actually, I retried and it can remain empty.
• The deployment target should be updated to 10 or 11 in the export template (although technically not necessary. I was able to deploy to iOS 12 with a target of 9).

StoreKit was already added in my case.

[akien-mga]

CC @bruvzg - I think some of these items have been implemented since then, is the current state good enough to close this issue or is there more validation that could be done?