[Feature Request]: Debug mode in teal apps

### Feature description

Outcome of this: https://github.com/insightsengineering/teal/issues/737#issuecomment-1291776635

As an end-user of an app
I don't want to have PID, Session Info and other technical metadata displayed in my GUI **on default**. However, I do want to have those information in case of errors in order to troubleshoot efficiently. I want to be able to turn-on a _debug mode_ interactively (i.e. when the app is initialised already) to get those.

When debug-mode is on then:
- unhide sessioninfo
- unhide debug info (new feature: https://github.com/insightsengineering/teal/issues/906)
- change logger to debug level

Implementation-wise we might use https://github.com/Appsilon/shiny.info. I can see it's missing some features such as session info display or custom callback functionality to call set logging level but we can either request or develop it.
We might also enter this on a key sequence.

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