Fix archiving/backup, update pdf library, clean up Dockerfile

[squ1rr3lly]

Everything now runs smoothly with docker-compose and the shaark Dockerfile would be more usable in other environments. I think this is production-ready, and would even be able to scale in a K8s/ECS/etc. deployment. I also made some code updates outside of just Docker, primarily switching the library used for PDF archiving to something that seemed better supported (spatie/browsershot).

Main changes:

Code:

• Replaced nesk/puphpeteer with spatie/browsershot; seems better supported and Shaark uses a lot of other spatie packages. I think this will be much easier to maintain with same functionality.
• The PDF Archive test gets http://example.com instead of app->(home)

Dockerfile:

• Updated image to php:alpine
• Chromium and spatie/browsershot for archiving
• Install youtube-dl for archiving
• Created regular user "shaarkuser" that runs the server with necessary capabilities set on entrypoint script; no longer have to run as root
• Set up crontab for backups

docker-compose:

• made the app/storage directory a volume; stores archives, backups, and all settings through rebuild/redeploy
• SHAARK_ADMIN_PASSWORD env variable allows setting initial admin user pass; defaults to "secret"
• Sets random mysql root password

Entrypoint:

• Cleaned up logic for determining when migrations/seeding should be performed
• Starts the artisan work queue