Flatpak: Initial support and underpinnings Part I

[yveszoundi]

Background

There was a discussion about Flatpak support and how to approach it going forward ( https://github.com/rimerosolutions/entrusted/discussions/42). This issue will actually implement the envisioned solution.

Request

• Simpler Flatpak support without embedding a virtual machine and a Web server
• Ability to easily keep the Flatpak version up to date for new releases

Overall changes

• [x] Refactor the main "Document Processing Component" (entrusted-container) to accept command-line arguments
• [x] Allow the UI to invoke directly the main document processing component without going through podman or docker
• [x] Refactor new gvisor support for alignment (Live CD specific feature)

References

• https://github.com/rimerosolutions/entrusted/discussions/42
• Flatpak main page
• Flathub portal