fixed arm64 build and slimmed down image

Credits for the slimming goes to https://github.com/chazlarson

Dockerfile

@@ -1,18 +1,20 @@
 FROM python:3.9-slim
 ENV TINI_VERSION v0.19.0
-ADD https://github.com/krallin/tini/releases/download/${TINI_VERSION}/tini /tini
-RUN chmod +x /tini
+COPY . /
 RUN echo "**** install system packages ****" \
  && apt-get update \
  && apt-get upgrade -y --no-install-recommends \
  && apt-get install -y tzdata --no-install-recommends \
- && apt-get install -y gcc g++ libxml2-dev libxslt-dev libz-dev
-COPY requirements.txt /
-RUN echo "**** install python packages ****" \
+ && apt-get install -y gcc g++ libxml2-dev libxslt-dev libz-dev wget \
+ && wget -O /tini https://github.com/krallin/tini/releases/download/${TINI_VERSION}/tini-"$(dpkg --print-architecture | awk -F- '{ print $NF }')" \
+ && chmod +x /tini \
  && pip3 install --no-cache-dir --upgrade --requirement /requirements.txt \
- && apt-get autoremove -y \
+ && apt-get --purge autoremove wget gcc g++ libxml2-dev libxslt-dev libz-dev -y \
  && apt-get clean \
+ && apt-get update \
+ && apt-get check \
+ && apt-get -f install \
+ && apt-get autoclean \
  && rm -rf /requirements.txt /tmp/* /var/tmp/* /var/lib/apt/lists/*
-COPY . /
 VOLUME /config
 ENTRYPOINT ["/tini", "-s", "python3", "plex_meta_manager.py", "--"]