Add image optimization tools to ddev web image

.ddev/web-build/Dockerfile

@@ -0,0 +1,3 @@
+ARG BASE_IMAGE
+FROM $BASE_IMAGE
+RUN apt-get update && DEBIAN_FRONTEND=noninteractive apt-get install -y -o Dpkg::Options::="--force-confold" --no-install-recommends --no-install-suggests jpegoptim optipng gifsicle