Define new Phase Descriptions

[mxgrey]

As part of open-rmf/rmf_ros2#107 we should start defining the Descriptions of the new Phase types.

We could start immediately on these task types:

• PerformAction (we will need the Description to have a parameter for an estimated duration for the action)
• ParkUntil (we will need the Description to have a parameter for an estimated duration of the parking)
• Call
• SMS
• RepeatN
• While (we will need the Description to have a parameter for an estimated number of repetitions so the planner can deal with this phase)
• ParallelGroup

This phase will require #42 before we can support it:

• RepeatIndefinitely

The APIs for these different phase Descriptions should be put into the rmf_task_sequence/phases include directory.

[mxgrey]

On this topic, maybe the Phases that are supposed to be repeaters shouldn't be phases, but instead we should incorporate it into the rmf_task_sequence::Task::Builder API, e.g. by providing add_repeated_phase and add_phase_while functions.