Use the orchestration agents prompt on an epic

Problem/Motivation

An orchestration agent is supposed to be the building block of the whole project and the system prompt in it is suppose to give context to how the orchestration of an epic is being split up into task.

However, currently this is using the old system from Minikanban, with a txt file prompt and then just feeding the possible agents to use.

Proposed resolution

* Switch over this to use the actual orchestration agent in `generateEpicToTaskPrompt`.
* Make sure that the orchestration agent is returning the agents and tasks it initially wants to create tasks for.
* (Possibly here or follow up task). Let the orchestration agent check the epic, when all tasks are set to done, to check if more follow up tasks are needed.