[Feature request] Prevent ns doctor from re-installing packages/modules already installed

Environment

• macOS Catalina 10.15.5, using an account having the administrator privileges
• CLI: 7.0.11 (iOS and Android setup)
• Your current package manager is npm 6.14.8
• XCode Version: 12.2 (12B45b)

With such a result from ns doctor :

✔ Getting environment information 

There seem to be issues with your configuration.
✔ Getting NativeScript components versions information...
✔ Component nativescript has 7.0.11 version and is up to date.
✔ Your ANDROID_HOME environment variable is set and points to correct directory.
✔ Your adb from the Android SDK is correctly installed.
✔ The Android SDK is installed.
✔ A compatible Android SDK for compilation is found.
✔ Javac is installed and is configured properly.
✔ The Java Development Kit (JDK) is installed and is configured properly.
✔ Xcode is installed and is configured properly.
✔ xcodeproj is installed and is configured properly.
✔ CocoaPods update is not required.
✔ Your current CocoaPods version is newer than 1.0.0.
✔ Python installed and configured correctly.
✔ The Python 'six' package is found.
✔ Xcode version 12.2.0 satisfies minimum required version 10.
✖ WARNING: CocoaPods is not installed or is not configured properly. 
 You will not be able to build your projects for iOS if they contain plugin with CocoaPod file.
To be able to build such projects, verify that you have installed CocoaPods (`sudo gem install cocoapods`). 

It would be appreciated for successfully installed packages/modules to not be re-installed again. At worst, to offer the user a possibility to select NO on an individual basis. Re-installing sometimes is a huge burden on a limited bandwidth Internet connection, and it also wastes a huge amount of time.

從 ns doctor 命令及其套件/模組檢查開始，在回報的 npm 6.14.8 環境中重現該行為。追蹤安裝前如何偵測已安裝的元件；完成標準是現有套件不會被重新安裝，且使用者可以在需要時拒絕個別的安裝。