Be able to add and remove a service on an existing goal
Let's say I have a fitbit goal to walk 10,000 steps a day.
Then maybe my fitbit breaks, but I find that my phone will count my steps that I take with it through the day, so I want to start entering manually based on that number.
I should be able to go to my goal and switch from using fitbit to update that goal's progress to removing fitbit from the goal and entering it manually.
On the flip side, if I start by entering my steps manually based on the value from my phone, then get a fitbit, I should be able to add the fitbit to start tracking the current goal right away, rather than having to make a new goal and losing all my tracked progress from the previous goal.