Special handling for experimental features

[Gedochao]

Is your feature request related to a problem? Please describe. Some of the features available in Scala CLI are experimental and non-ideal UX should be expected, but they are not marked as such. An example can be the --spark or the incoming Markdown support.

Describe the solution you'd like We should document the features which are experimental as such both in the docs and in the relevant command line help. We should log warnings when such features are being used. However, it should be possible for the user to have a global setting which would silence those warnings (similarly to how --interactive can be set permanently.

Describe alternatives you've considered The ideal solution would be to have centralised handling for experimental commands and options in case-app, but for the time being, implementing something in scala-cli should be easier.