Docker image, Bluesky video support, prebuilt binaries

• Docker: a docker image is now available at https://hub.docker.com/r/klausi/mastodon-bluesky-sync . Check INSTALL.md how to run it!
• Prebuilt binaries are now automatically attached to releases here - please test!
• ffmpeg is a new external dependency to support Bluesky video conversion
• OpenSSL has been removed as dependency - prebuilt binaries should work now on more Linux systems out of the box.

🚀 Features

• (bluesky) Add support for video attachment upload
• (bluesky) Shorten links to use 300 character limit better
• (bluesky) Support image attachments on quote posts
• (bluesky) Support Bluesky video stream embeds
• (bluesky) Extract video attachment from Bluesky quote post
• (docker) Add Docker image
• (github) Add action to create release binaries

🐛 Bug Fixes

• (sync) Fix Bluesky link replacements with multiple links
• (mastodon) Count links only as 32 characters in posts send to Mastodon
• (bluesky_richtext) Fix link detection to only go for http
• (bluesky) Extract link embed URL if it is not in the post directly
• (sync) Do not escape user name mentions, Bluesky does not auto-link them

🚜 Refactor

• (clippy) Apply Clippy recommendations
• (post) Make file operations async
• (openssl) Remove OpenSSL dependency
• (github) Modernize github action testing