Update docker file to add mechanicalsoup python library (#1688)

Add a new python library mechanicalsoup to the docker container.
There is a pending pull request in the Community scrapers for the Ifeelmyself that uses this library so it might be worth including it in the container.
This should add ~100k to the size of the container.

docker/ci/x86_64/Dockerfile

@@ -11,7 +11,7 @@ RUN if [ "$TARGETPLATFORM" = "linux/arm/v6" ];   then BIN=stash-pi; \
 ENV DEBIAN_FRONTEND=noninteractive
 RUN apt update && apt install -y python3 python-is-python3 python3-requests python3-requests-toolbelt python3-lxml python3-pip && pip3 install cloudscraper
 FROM ubuntu:20.04 as app
-run apt update && apt install -y python3 python-is-python3 python3-requests python3-requests-toolbelt python3-lxml ffmpeg && rm -rf /var/lib/apt/lists/*
+run apt update && apt install -y python3 python-is-python3 python3-requests python3-requests-toolbelt python3-lxml python3-mechanicalsoup ffmpeg && rm -rf /var/lib/apt/lists/*
 COPY --from=prep /stash /usr/bin/
 COPY --from=prep /usr/local/lib/python3.8/dist-packages /usr/local/lib/python3.8/dist-packages