Feature request: Use all funds to open channel

[chill117]

At present here are the steps to utilize all on-chain funds when opening a channel:

• Input / scan a node URI
• Switch to sats (not fiat)
• Manually input the total number of sats in the on-chain balance
• Try to open channel
• Fails with error message - this message is only visible for a couple seconds
• Calculate the difference between the two amounts shown in the error message
• Subtract the difference from the total on-chain sats balance
• Manually input the amount into the field again
• Try to open channel
• Fails again because I did the above steps too slowly and the internal caches updated the reserve amount or network fee rate estimate
• Try the above steps again until it works

This is not very nice. Is it possible to take whatever calculations the app is doing to generate that error message and instead provide a button in the UI that let's the user simply auto-calculate the maximum allowable opening channel amount?

Thanks for your work on the app!