metamask-mobile feat: Update onboarding copy

Description

Updates the onboarding text.

This PR is against the new-privacy-policy-toast since they need to go together

Related issues

Fixes: https://github.com/MetaMask/MetaMask-planning/issues/2220

Manual testing steps

Start onboarding a new user
Check that the notice has the new copy

Screenshots/Recordings

Before

After

Pre-merge author checklist

[ ] I’ve followed MetaMask Coding Standards.
[ ] I've completed the PR template to the best of my ability
[ ] I’ve included tests if applicable
[ ] I’ve documented my code using JSDoc format if applicable
[ ] I’ve applied the right labels on the PR (see labeling guidelines). Not required for external contributors.

Pre-merge reviewer checklist

[ ] I've manually tested the PR (e.g. pull and build branch, run the app, test code being changed).
[ ] I confirm that this PR addresses all acceptance criteria described in the ticket it closes and includes the necessary testing evidence such as recordings and or screenshots.

Apr 16 '24 10:04 jonybur

CLA Signature Action: All authors have signed the CLA. You may need to manually re-run the blocking PR check if it doesn't pass in a few minutes.

Apr 16 '24 10:04 github-actions[bot]

for the CLA signature check that needs to pass above, I believe I followed the github actions comment above https://github.com/MetaMask/metamask-mobile/pull/9256#issuecomment-2058799917