Use git via CLI when building with rust

We get random errors, when rust is building, stating that

  failed to fetch https://github.com/rust-lang/crates.io-index

This appears to [be known][1] and will be fixed in the future. Until
then the suggested workaround is to use git that is installed on the
system instead.

[1]: rust-lang/cargo#9187

src/.dockerignore

@@ -0,0 +1,2 @@
+**/nginx_secrets/
+/nginx_conf.d/example_server.conf

src/Dockerfile

@@ -17,6 +17,9 @@ ENV CERTBOT_DNS_AUTHENTICATORS \
     route53 \
     sakuracloud
 
+# Workaround for https://github.com/rust-lang/cargo/issues/9187
+ARG CARGO_NET_GIT_FETCH_WITH_CLI true
+
 # Do a single run command to make the intermediary containers smaller.
 RUN set -ex && \
 # Install packages necessary during the build phase (for all architectures).
@@ -25,6 +28,7 @@ RUN set -ex && \
             build-essential \
             cargo \
             curl \
+            git \
             libffi7 \
             libffi-dev \
             libssl-dev \
@@ -45,6 +49,7 @@ RUN set -ex && \
             build-essential \
             cargo \
             curl \
+            git \
             libffi-dev \
             libssl-dev \
             python3-dev \

src/Dockerfile-alpine

@@ -17,13 +17,17 @@ ENV CERTBOT_DNS_AUTHENTICATORS \
     route53 \
     sakuracloud
 
+# Workaround for https://github.com/rust-lang/cargo/issues/9187
+ARG CARGO_NET_GIT_FETCH_WITH_CLI true
+
 # Do a single run command to make the intermediary containers smaller.
 RUN set -ex && \
 # Install packages necessary during the build phase (for all architectures).
     apk add --no-cache \
         cargo \
         curl \
         findutils \
+        git \
         libffi \
         libffi-dev \
         libressl \
@@ -48,6 +52,7 @@ RUN set -ex && \
     apk del \
         cargo \
         curl \
+        git \
         libffi-dev \
         libressl-dev \
         python3-dev \