[Feature request] SwapServer - custom static fees, asymmetric fees, swap minsize config

[Go-ops-sw]

Description

Feature 1 - Custom static fees
It would be great if one could set static fees together with dynamic fees. Since the on-chain fees as well as LN fees are bit unpredictable, the swap server operator may see small negative returns when the dynamic swap fee is set low and the swap size is small. Allowing to set a custom extra static fee could compensate for these, allowing the operators to set very small swap fees without seeing negative returns.

Feature 2 - Asymmetric fees
It would be great if one could set different dynamic fee for forward and reverse swaps. Since boltz.exchange has highly asymmetric fees, it would be great if Electrum swap server could match that so that we can stay competitive in both directions.

Feature 3 - Config for minimum swap size
It would be great if one could set minimum size of swap size (ideally, one setting per swap direction). Some operators may be interested in having very low fees (for example for the forward swap - see asymmetric fees above) but in such cases it may be reasonable to have a minimum limit on the size of the swap.

[ecdsa]

Asymmetric fees would be great to have in the next iteration of the protocol.
We should also simplify the list of providers in the GUI, by showing fees and liquidity in only one direction
Currently, the presence of two "max amount" columns (and their wrong naming) is confusing.

The user config could also save two servers, one for each direction.