docker: enable profiling with xdebug

docker/php/Dockerfile.profile

@@ -0,0 +1,16 @@
+# syntax = devthefuture/dockerfile-x
+INCLUDE ./docker/php/Dockerfile
+
+RUN apk add --no-cache \
+        linux-headers \
+        $PHPIZE_DEPS \
+    && pecl update-channels \
+    && pecl install xdebug \
+    && docker-php-ext-enable xdebug \
+    && apk del \
+        linux-headers \
+        $PHPIZE_DEPS \
+    && rm -rf /var/cache/*
+
+ENV XDEBUG_OUT_DIR=/var/www/xdebug_out
+CMD [ "bootstrap.sh" ]