fix(install): respect XDG_CONFIG_HOME (#839)

Apply the same logic that is used in
_spicetify/cli/src/utils/path-utils.go:GetSpicetifyFolder_.
$SPICETIFY_CONFIG_DIR is now, in order :
- $SPICETIFY_CONFIG
- $XDG_CONFIG_HOME/spicetify
- $HOME/.config/spicetify

This fixes a bug when installing `spicetify` and `marketplace` with a custom
$XDG_CONFIG_HOME, making the marketplace theme and custom app invisible to
spicetify.

resources/install.sh

@@ -23,7 +23,10 @@ echo "FETCHING Version $tag"
 download_uri=$releases_uri/download/v$tag/marketplace.zip
     default_color_uri="https://raw.githubusercontent.com/spicetify/marketplace/main/resources/color.ini"
 
-SPICETIFY_CONFIG_DIR="${SPICETIFY_CONFIG:-$HOME/.config/spicetify}"
+SPICETIFY_CONFIG_DIR="$SPICETIFY_CONFIG"
+if [ -z "$SPICETIFY_CONFIG_DIR" ]; then
+	SPICETIFY_CONFIG_DIR="${XDG_CONFIG_HOME:-$HOME/.config}/spicetify"
+fi
 INSTALL_DIR="$SPICETIFY_CONFIG_DIR/CustomApps"
 
 if [ ! -d "$INSTALL_DIR" ]; then