[FEATURE] Ability to expose application ID to manifest

[filmaj]

This was originally requested on the Community Workspace by @djmgit

For some developers, an app has only a few, well-known installations: staging, test, production. For this kind of app setup, the question is: how can one conditionally set the application icon depending on the workspace / installation target?

Off the top of my head idea: expose the app ID (which could potentially be null or undefined in the case of a brand-new installation) to get get-manifest hook.