Implement API endpoint for creating an action

[arcrose]

Dependent on #443.

This endpoint will be used to specify a module to run in an action, the agents to target, and any other configuration data for the action to construct. The action must not be dispatched immediately but, rather, be retained by the client daemon for some period of time. During this time, the investigator may wish to make alterations to the action they created, scrap it, etc.