feat: Reduces docker image size

Drastically reduces Docker image size by changing from discord.py base
image to python base image, reducing number of redundant dependencies
downloaded. (Also because migration to discord.py v2)

task: none

Dockerfile

@@ -1,4 +1,16 @@
-FROM gorialis/discord.py
+FROM python:3.9.1-alpine
+
+RUN \
+    echo "http://dl-8.alpinelinux.org/alpine/edge/community" >> /etc/apk/repositories && \
+    echo "http://dl-8.alpinelinux.org/alpine/edge/testing" >> /etc/apk/repositories
+
+# Install basic dependencies
+RUN \
+    apk --no-cache add -q git cloc openssl openssl-dev openssh alpine-sdk bash gettext sudo build-base gnupg linux-headers xz
+
+# install discord.py - this done outside of requirements.txt to lower build times  
+RUN pip3 install git+https://github.com/Rapptz/discord.py@e0341c9#egg=discord.py
+
 WORKDIR /app
 COPY . .
 RUN pip install -Ur requirements.txt