image: T4516: Added system image tools
This commit adds the whole set of system image tools written from the scratch in
Python that allows performing all the operations on images:
- check information
- perform installation and deletion
- versions management
Also, it contains a new service that will update the GRUB menu and keep tracking
its version in the future.
WARNING: The commit contains non-reversible changes. Because of boot menu
changes, it will not be possible to manage images from older VyOS versions after
an update.
(cherry picked from commit 8f94262e8fa2477700c50303ea6e2c6ddad72adb)