Add option to exclude apps from build pipeline and/or deployment #1618

Currently, it's only possible to exclude apps like Insights and Swagger using JSON configuration files.
Preferably we'd like to exclude the npm build process for some of these apps, to drastically decrease build times.
For example, some custom projects might not need these additional apps.

This issue did arise along with the upcoming UI documentation (see PR #1586),
where an additional app is being built, and deployed on the web server.
We should consider making apps optional using environment variables and/or pipeline options.

Needs investigation on what solution fits best here.