[v3] wails3 generate icons - default variable values

[mkko120]

Is your feature request related to a problem? Please describe.

When trying to create an icon, it requires arguments of filenames for generated icons, such as ./build/windows/icon.ico. There is nothing in the documentation (afaik) that tells what those should be.

Describe the solution you'd like

1. Document default values for each parameter (-windowsfilename and -macfilename)
2. Possibly add a default behavior to the command when none of the parameters above are specified, e.g.:

• user uses command wails3 generate icons
• wails3 tool looks for appicon.png in build directory
• wails3 tool automatically generates the required windows and darwin icon files in windows and darwin directories

Same principle with -input option but instead of appicon.png it selects the icon from input parameter.

Describe alternatives you've considered

No response

Additional context

No response