Merge master and build images with linuxserver/ffmpeg support

[lizardfish0]

See #50 for most of the changes, but this version will also:

• Combine build functionality into the main branch.
• Cleanup and conslidate Dockerfile/s6 run file. I think it makes most sense to do package setup (apt/apk installs) and git operations in the Dockerfile. Then, the s6 run file handles all the SMA-specific business logic of setting up the python venv and installing python packages.

This setup makes using build args a little more straightforward. You can now do the following:

Basic setup.

services:
  sonarr:
    image: mdhiggins/sonarr-sma
    container_name: sonarr
    restart: unless-stopped
    volumes:
      - ../volumes/data/sonarr:/config
      - ../volumes/config:/usr/local/sma/config

Results in linuxserver/sonarr:latest with linuxserver/ffmpeg:latest.

---

Build from a specific sonarr image (you need to make sure sonarr/ffmpeg OS is compatible, but that's already the case).

services:
  sonarr:
    image: mdhiggins/sonarr-sma
    build:
      context: mdhiggins/sonarr-sma
      args:
        sonarr_tag: 3.0.9
    container_name: sonarr
    restart: unless-stopped
    volumes:
      - ../volumes/data/sonarr:/config
      - ../volumes/config:/usr/local/sma/config

Same but now you have v3.0.9.

---

Use jrottenberg (same warning as above).

services:
  sonarr:
    image: mdhiggins/sonarr-sma
    build:
      context: mdhiggins/sonarr-sma
      args:
        ffmpeg_source: jrottenberg/ffmpeg
        ffmpeg_tag: 5.1-nvidia
    container_name: sonarr
    restart: unless-stopped
    volumes:
      - ../volumes/data/sonarr:/config
      - ../volumes/config:/usr/local/sma/config

---

Override with static ffmpeg.

services:
  sonarr:
    image: mdhiggins/sonarr-sma:latest
    container_name: sonarr
    restart: unless-stopped
    environment:
      SMA_FFMPEG_URL: https://johnvansickle.com/ffmpeg/releases/ffmpeg-release-amd64-static.tar.xz
    volumes:
      - ../volumes/data/sonarr:/config
      - ../volumes/config:/usr/local/sma/config