Add the ability to compose the legend name using values ​​contained in the attributes

[albertograva]

Feature description

Hi everyone!
I think it would be very useful if in the symbology panel we could customize the legend name for each symbol using the expression builder.
In my opinion it would be very useful because I often use data that has the legend entry inserted in attribute fields other than the categorization one and this avoids having to manually edit every single entry.
In the attached examples I illustrate what the panel could look like in "categorized" mode and "ruled-based" mode, in the other simbology mode I think it would be similar to categorized.

Thanx a lot!

Additional context

[albertograva]

@ghtmtt