feat: declare and export the original user path

@mmorenoregalado proposes to maintain consistency among different nodes and sessions through CodelyTV@8dc02e4 and CodelyTV#172, which generates a side-effect for users and adds a possible code smell in the future because it introduces an if-else pattern based on a condition that users may not expect. Also it doesn't allow the user to employ other environment variables, so we apply the template engine ideas and differentiate the application of Bash expansion.

installer

@@ -67,9 +67,10 @@ _w "~ │ 🚀 Welcome to the ${green}dotly${normal} installer! │ ~"
 _w "  └────────────────────────────────────┘"
 _w
 _q "Where do you want your dotfiles to be located? (default ~/.dotfiles)" "DOTFILES_PATH"
-DOTFILES_PATH="${DOTFILES_PATH:-$HOME/.dotfiles}"
-DOTFILES_PATH="$(eval echo "$DOTFILES_PATH")"
+UNEXPANDED_DOTFILES_PATH="${DOTFILES_PATH:-\$HOME/.dotfiles}"
+DOTFILES_PATH="$(eval echo "$UNEXPANDED_DOTFILES_PATH")"
 export DOTFILES_PATH="$DOTFILES_PATH"
+export UNEXPANDED_DOTFILES_PATH="$UNEXPANDED_DOTFILES_PATH"
 
 dotly_inner_path="modules/dotly"
 export DOTLY_PATH="$DOTFILES_PATH/$dotly_inner_path"