[Cashtab] Prompt for auth only if enabled - p2/2, implementing

Summary:
T2874

Depends on D12874

Stop asking new users for auth the first time they use the app. Feature must be enabled manually.

Test Plan:
npm run build
netlify deploy

Test this on mobile at your deployed address

Open. Create wallet. Go to settings pages and enable app lock. Use the app with app lock.
Repeat in an incognito window. Confirm signup flow does not ask for auth.

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D12877