Disable recommends in python-base and python-builder

We disable these on our VM images, so might as well make our
container images follow suit. Could make them a smidge smaller.
Also do it in the gerrit-base image.

Change-Id: Iba60cf5c7009d57c4910f9e4464aff9231598ad6

docker/python-base/Dockerfile

@@ -15,6 +15,8 @@
 
 FROM docker.io/library/python:3.7-slim
 
+RUN echo 'APT::Install-Recommends "0";' > /etc/apt/apt.conf.d/95disable-recommends
+
 RUN apt-get update \
   && apt-get install -y dumb-init libjemalloc2 \
   && apt-get clean \