[Orgs] Implement sign in button

[usame-algan]

Links

Epic on Notion: https://www.notion.so/safe-global/Org-onboarding-flow-1208180fe57380078591f5380a0c5d2a

What must be done

• Adjust the current sign in button to match the design of the continue with wallet button
• Handle disconnected wallet fallback

Designs/sketches

How to test it

• If the user has no connected wallet they should not sign in but instead connect first
• If they are connected the sign in button should look like the continue with wallet button

[francovenica]

@jmealy

Question. This ticket says we should handle the disconnect (which currently works in the RC), but shouldn't also handle changing the wallet's owner?
Currently if you switch owners in your MM extension, you are still logged in as previous user. You are forced to disconnect and then reconnect with already the user you want selected in MM.