Update frontend to better integrate secret-to-token behaviour

[ddamico]

** update react-hook-form either before this or as part of it, looks like there are changes in there that relate specifically to some of the behaviour changes we want to do https://react-hook-form.com/migrate-v6-to-v7/ **

Per conversation on Apr. 17th, the plan here is to...

• validate input on submission instead of on change
• switch the form label to token or api secret
• add some copy explaining that we’re not going to retain secret, but will use it to generate token
• update the field value to the "cleaned" value returned from the validation endpoint