Investigate fixed fee viability

[ureeves]

Summary

It might be viable to (re)introduce a fixed fee for simple transfers, for both better user experience and client-side note proliferation mitigation.

Possible solution design or implementation

A fixed fee is fairly easy to introduce, especially given the atomicity of transactions. Care should be taken to not re-introduce transaction re-execution into execute state transition (EST).

Additional context

But I still believe that having a fixed fee for transfer would be a benefit for the network. Does it worth to reintroduce it?
Originally posted by @herr-seppia in #1125 (review)

[HDauven]

@ureeves @ZER0 @herr-seppia @miloszm Is this still relevant? Do we need to discuss this?