Make the Launcher available via Debian's APT package manager

[TSchmiedlechner]

Is your feature request related to a problem? Please describe.

Currently, users need to manually download the Launcher, e.g. from the Portal. This works in many cases, but using the inbuilt package managers to install software is far mor common on Linux.

Describe the solution you'd like

We should support using the APT package manager to install the Launcher, to e.g. allow something like this:

sudo apt install fiskaltrust-launcher

Additional context

As most of our Linux users either operate Debian or one of it's derivatives like Ubuntu, we should start with supporting APT and .deb packages, and add other package managers like YUM later on.

As it's pretty hard to get packages into the official Debian repos, I'd suggest to introduce our own repository, like e.g. Microsoft and Mono do it for their packages. This would mean that to install our software, you'd first need to add the package source and the key (with one command each), and can use the command shown below afterwards.

Steps to take

• Create an APT repository, e.g. on an Azure Blob Storage (I found this guideline pretty useful)
• Build .deb packages in the build pipeline (also described in the tutorial)
• Push the packages to the package repository in the deployment pipeline
• Update docs to explain how this can be used
• Disable the self-update and instead print a message that a new version is available

Related to #17