CI: add release workflow for building binaries

[daywalker90]

This PR adds a workflow to create a release with release binaries.

It cross compiles for:

• x86_64-unknown-linux-gnu
• aarch64-unknown-linux-gnu
• armv7-unknown-linux-gnueabihf

using cross and only requires glibc >= 2.31.

I packaged teosd and teos-cli together while watchtower-client is in an extra archive.

For better cross compatibility i removed the dependency to the system specific openssl and replaced it with rustls-tls.

For this job to trigger you have to push an annotated tag. It will only trigger on tags that represent final releases.

This project does not have a CHANGELOG.md so i commented in two methods on how to provide the content body for the release:

• either create a CHANGELOG.md that adheres to the formatting of keepachangelog
• or use the message from the annotated tag (can also be a file with -F)

You can of course also just edit the release body manually on the website but then it won't show in the notification email that is send to users.