Add missing information on ?session page

[pyltime]

The documentation for the session object in ?shiny::session or at https://shiny.rstudio.com/reference/shiny/1.5.0/session.html does not mention the values of session$user or session$groups, which can be used with Shiny Server Pro or RStudio Connect to customize user privileges (as we document on the Shiny site here: https://shiny.rstudio.com/articles/permissions.html or in the Connect user guide here: https://docs.rstudio.com/connect/user/shiny/#user-meta-data). It would help to have these spelled out directly as specific options in the official documentation so that it exists as a standard reference point for users.

[cpsievert]

Some other things we should add:

• setCurrentTheme(), getCurrentTheme()
• Output info (and link to getCurrentOutputInfo())?
• The new session-level options? (and link to getShinyOption()?)

https://github.com/rstudio/shiny/blob/81a8ec3ce14c1a88bd48057591d560536a321ac4/R/shiny.R#L665