Revert to installing yq via pip.

Dockerfile

@@ -1,3 +1,5 @@
+# syntax = docker/dockerfile:experimental
+
 # Dockerize releases use a different label for arm64 than ${TARGETARCH}, so we need to
 # explicitly set ${DOCKERIZE_ARCH} in a base image for each platform.
 
@@ -16,14 +18,16 @@ RUN apk update \
         bash \
         jq \
         nginx \
+        py3-pip \
         tini \
-        yq \
     && rm -rf /var/cache/apk/*
 
 # Do NOT use dockerize 0.6.1 due to https://github.com/jwilder/dockerize/issues/125
 ENV DOCKERIZE_VERSION=0.6.0
 RUN wget -nv -O - "https://github.com/jwilder/dockerize/releases/download/v${DOCKERIZE_VERSION}/dockerize-linux-${DOCKERIZE_ARCH}-v${DOCKERIZE_VERSION}.tar.gz" | tar -xz -C /usr/local/bin/ -f -
 
+RUN --mount=type=cache,id=nginx-proxy-redirect,target=/root/.cache/pip pip install --no-cache-dir yq
+
 ENV PATH="/opt/nginx-proxy-redirect/bin:$PATH"
 
 EXPOSE 80