Rebuilt to use python:slim instead of buster

Reduced footprint of the image to less than a quarter from before.
Compatibility with Opus and Numpy still maintained as it is Debian based

app/Dockerfile

@@ -1,7 +1,7 @@
-FROM python:3.9.6-slim
-RUN apt-get update -y && apt-get upgrade -y && apt-get install libopus0 -y
+FROM python:slim
 COPY . /usr/src/app
 WORKDIR /usr/src/app
-RUN pip install --upgrade pip
-RUN pip install -r requirements.txt
+RUN apt-get update -y && apt-get upgrade -y && apt-get install libopus0 -y && \
+	pip install --upgrade pip && pip install -r requirements.txt && \
+	apt-get autoremove -y
 CMD python3 -u ./bot.py