Add customizable BTC confirmation threshold

[Dianaaiym]

Implement a customizable confirmation threshold setting in the Blockchain Settings - Bitcoin section of Unstoppable Wallet. This feature will allow users to define the number of confirmations required for Bitcoin transactions to be considered valid, providing flexibility between security and transaction speed.

UI Placement:

• Add a new option under Blockchain Settings - Bitcoin to adjust the number of confirmations required for Bitcoin transactions.
• Include a dropdown list or input field for users to choose or enter a custom number of confirmations (e.g., 1, 3, 6, or user-defined).
• Provide clear descriptions and tooltips to explain the implications of changing this setting, especially regarding security risks and trade-offs.

[Dianaaiym]

#6036