[native] Introduce ConnectEthereum screen

Summary:
For now it's going to look rather messy. In subsequent diffs I will:

1. Fix up the styling and spacing of the buttons
2. Replace the text with an ordered list
3. Introduce the Ethereum icon from the designs

Depends on D7725

Test Plan:

Reviewers: atul, ginsu

Reviewed By: atul

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D7729