[Feature] Be able to edit the values pre-defined on send sats window buttons

### Feature description

I never use the values pre-defined on send sats window. I would like to be able to edit the values to values that I usually use.


### Describe the solution

I would like to be able to edit the values for values that I usually use.

### Describe alternatives

_No response_

### Additional context

_No response_

### Are you working on this?

No

No file or test is named. Start by locating the send sats window and its pre-defined amount buttons, then trace how the wallet stores user preferences. Define the editing interaction and persistence behavior, and consider adding or updating UI tests to verify that customized values appear after reopening the window.

Written by the indexing model from the issue text.