Merchant Upgrade flow Step 3: Update users to Level 3 Account - Merchant

[brh28]

Merchant details are being entered in https://github.com/lnflash/merchant-signup and stored in Supabase.

Steps:

• create a mutation on the Admin-api to upgrade user account to Level 3 (perhaps updateUserLevel)
• Cashout feature checks for level 3

Relates to - lnflash/flash-mobile#396

[Nodirbek75]

@brh28 Can we also add an account upgrade status? Level 3 users will remain pending until they confirm the test transaction.