Update DXF export section

[gacarrillor]

• Add paragraph for export/import DXF export settings to/from XML
• Rename output layer name.
• Add details for Input layer parameter in Export layers to DXF alg.

Fix #8998
Fix #9028
Fix #9045

[gacarrillor]

@DelazJ

I've added a little note on the processing alg to mention new options in "Input layers" parameter.

I was wondering if that's enough to also consider #9045 fixed or if we should add a screenshot like the one you can find in #9045's description.

[DelazJ]

I'm not sure we need a screenshot but I'd rather see something in the vein of what was done for align rasters "layer inputs", i.e. how you get to the options and what they really are (name, type, default, ... information that helps to call them in a code, as any other parameter)

[gacarrillor]

I'm not sure we need a screenshot but I'd rather see something in the vein of what was done for align rasters "layer inputs", i.e. how you get to the options and what they really are (name, type, default, ... information that helps to call them in a code, as any other parameter)

Looks great, thanks for the pointer.