`PSNodeJob.ContentPipeline` should determine how content is served

[StartAutomating]

Currently, this is hardcoded into PSNode (and that's generally not ideal).

Essentially, if we are serving HTTP requests, our pipeline should be flexibly determinable by content type.

This will be a lookup table of content-type to a series of pipeline steps.

• Any [string] will be considered a command name.
• Any [ScriptBlock] will be considered a command.
• Any [Management.Automation.CommandInfo] will obviously be a command
• Anytime a new Command is encountered, it will become an .AddCommand or .AddScript
• Any [Object[]] will be considered arguments, and will become .AddArguments()
• Any [Dictionary] or [PSObject] will be considered parameters and will become .AddParameters()

Any commands referenced in this information should be added to the initial session state (preferably by importing their modules)

This relates to #970 (which will serve as the basis for the default values)