Use a LSPS1 provider instead of PMLSP for Alby shared node funds migration to open first channel

[rolznz]

• UI needs to be thought a bit - "Increase Receiving Capacity" page is not needed since we can auto-calculate the amount and just use the first suggested LSPS1 provider. All the user needs to do is confirm the channel purchase.
• requested amount should be (shared node amount + 500K) rounded up to nearest 1M sats.

[rolznz]

Updated Flow:

New "Open your first channel" flow which merges Migration + new channel in one go.

• Starts from the existing Checklist item "Open your first channel"
• Goes to a brand new page
• If the user has shared balance, calculate the amount (+500K, rounded up to nearest million), otherwise provide no value as the amount
• Requests an order using Alby Hub existing code, but to Alby's API as the LSP (Alby API is a proxy)
• If there is an invoice in the response:
  • If the user has shared node balance, use that to internally pay it
  • Otherwise show the user a QR code that they pay with a new wallet
• Go to the current channel order page and wait for the channel to open
• On the success screen, if the user has remaining shared balance, automatically migrate