Docs: Add More Details About Reporting Support for Containers

[MariaSemple]

There are currently instructions about when you should report support for containers, but not about why you should report support for containers. We should document the different behaviour that consumers of the Launcher will have when working with Plugins that support containers. Non-exhaustive list below:

• The consumer will set the ExposedPorts object on the Job, telling the plugin which ports it needs exposed to communicate with the Job.
• The consumer may modify how the Job is launched to account for container limitations. For example:
  • the IDE can be configured to create container users when the job starts.
  • the IDE can be configured to forward the current environment to the container
  • the IDE will disable project sharing in a containerized job context
  • the IDE will bind the session to a specific port, for the purposes of exposing the port
  • the IDE will enable proxying shiny apps through the R session so they still work without exposing more ports
  • the IDE can be configured to request that the container run as the root user
  • the IDE will disable project sharing in R sessions