Store API keys securely, not in settings.json

[hunter-nl]

Is your feature related to a specific framework or general for this extension
Not related to framework.

Is your feature request related to a problem? Please describe.
The API keys are stored now in the Visual Studio Code settings.json file as plain text. This is not secure!
Visual Studio Code’s SecretStorage for extensions is available to store things like API keys securely.

Describe the solution you'd like
Please update extension to not store the API keys in settings.json, but into the Visual Studio Code’s SecretStorage.

Additional context