Add yarn scripts for watching individual platforms for GUI connectivity example app

[amircybersec]

On my development workflow, I don't have Xcode installed (Ubuntu) and I am just building for android.

In package.json file in shared_backend directory, there's a line that says:

"build": "concurrently 'yarn:build:*' --kill-others-on-fail",

The --kill-others-on-fail flag sends a SIGTERM signal to other processes if one build process fails. Since I don't have Xcode installed, the following build process fails:

"build:ios": "gomobile bind -target ios,iossimulator -o output/SharedBackend.xcframework github.com/Jigsaw-Code/outline-sdk/x/examples/outline-connectivity-app/shared_backend",

This causes the other processes, including build:android to get killed.

As a result, the SharedBackend.aar & SharedBackend-sources.jar files don't get generated.

Please see the yarn log below:

[shared_backend]: [ios] gomobile: -target="ios,iossimulator" requires Xcode
[shared_backend]: [ios] yarn run build:ios exited with code 1
[shared_backend]: --> Sending SIGTERM to other processes..
[shared_backend]: [android] yarn run build:android exited with code SIGTERM
[shared_backend]: [nodemon] app crashed - waiting for file changes before starting...

In Android Studio, the following error is thrown:

Null extracted folder for artifact: ResolvedArtifact(componentIdentifier=SharedBackend.aar, variant=local file, variantName=null, artifactFile=/home/amir/ICFP/outline-sdk/x/examples/outline-connectivity-app/shared_backend/output/SharedBackend.aar, isTestFixturesArtifact=false, extractedFolder=null, publishedLintJar=null, dependencyType=ANDROID, isWrappedModule=false, buildMapping={__current_build__=/home/amir/ICFP/outline-sdk/x/examples/outline-connectivity-app/app_mobile/android})

Potential solution

I tried removing the --kill-others-on-fail flag and it seemed to work. I am not sure about the repercussions of this and whether there's a better solution.

[amircybersec]

BTW, I am not able to choose Labels for issues. IMHO it would be helpful to setup a GitHub Porject for Connectivity GUI App (and potentially other SDK related sub-projects) so that relevant issues can be assigned to the right Project. Using Projects can also help with feature/milestone planning, organized under Project tab.

[amircybersec]

This PR addressed this issue

#108

Thanks @daniellacosse 🙏