fix: ensure backup address is checksummed before submitting to backend

[truemiller]

@oaksprout mentioned he experienced errors when backup wallet address was not checksummed

fix ensures the address is checksummed in the background

• allows for non-checksummed input (as to not frustrate users)
• will send the checksummed address to middleware when creating a safe (to add as signer)

tried using validation rules on the Antd input, but transform and validator functions don't update input value. hence the validation on submit.

should resolve #331, Trello ticket

Video

(made a small fix mid way through, works as expected now)

checksumming.video.mp4

[mohandast52]

LGTM 🎉 , Going forward, it might be helpful to include some screenshots/videos or visualizations to ensure we don’t miss any UX details and to avoid potential regressions.