[FEAT] Determine font names from the aliases "serif", "sans-serif", "monospace"

### Description

Many people use these standard aliases in fontconfig to set their fonts system-wide. Fastfetch only displays the aliases. The real font names can easily be determined. For example, with a command like `fc-match -s ':family=monospace'`.

### Motivation

It's an enhancement to existing font fields.

### Additional context