Follow-up: use API endpoint for editing credit card

When editing a credit card, the first iteration was to render the Vue app within a <form> tag, then we submit the whole form.

A second iteration would be to remove the <form> tag and make the Vue app responsible for submitting the data to an API endpoint dedicated to updating the form (could be the same one we're currently using in the <form>).

Original discussion started in !1729:

• @jayswain started a discussion: (+2 comments)

  Question: Why do we render inside of a form wrapper? As we're passing the form URL down, I'm assuming we're using that in some axios request anyhow.

Note: I'd suggest a weight between 3-5, but it needs more investigation before deciding on a weight.