remove instance id from task show api

[burnettk]

right now it's:

/tasks/16/1deef7a0-59a5-4607-a840-30e7edb6f872

proposal:

add route to /tasks/1deef7a0-59a5-4607-a840-30e7edb6f872 and deprecate the old one.

we don't need the instance id for context. the task belongs to an instance. we don't need the instance id for permissions, since you don't want permissions at the instance level hopefully ever.