ENG-8468 Strengths form on profile not working properly

Problem

- When users save the CareerVisionForm, they get a 500 error

- Sentry log suggests it's a dict key access issue, where I did not make

provision for the strengths form to be empty when adding disabled to it

- In the first PR, I just initialize a list for the strengths field and then add

the new values to it IF they exist

- I was able to write a test that failed with out the fix, and passed with the

fix, so that gave me some confidence the situation was fixed

- Turns out there was a secondary problem with how I modified the form where the

strengths fields were not even added to the form if default attributes didn't

exist. That is fixed in ENG-8503