WISH: Add RSC_RSESSION_TIMEOUT_SUSPEND

[HenrikBengtsson]

Add environment variable RSC_RSESSION_TIMEOUT_SUSPEND to control:

• session-timeout-suspend: Indicates whether or not to suspend the session after the timeout has elapsed. Setting this to false will cause the session to quit instead of suspending to disk when the session times out. (Type: bool; Default: 1)

Source: https://docs.posit.co/ide/server-pro/rstudio_server_configuration/rsession_conf.html

This might be relevant for Issue #90.

[HenrikBengtsson]

Added support for RSC_RSESSION_TIMEOUT_SUSPEND without changing the default behavior.