Gns3-server

* Set setuptools to v60.6.0
* qemu_vm.py Linked node test.
* Fix dead link in README.rst Fixes 2022

* Add NixOS in list of distributions with a package

* Simpler Systemd service file. Ref 1996

* Fix unhandled KeyError exception when starting Docker container. Ref 1991

* Sort symbols by theme. Fixes https://github.com/GNS3/gns3-gui/issues/3230
* Fix memory percentage left warning. Fixes 1966
* Update affinity symbols. Fixes https://github.com/GNS3/gns3-gui/issues/3232

* Fix issue preventing to use custom nested symbols. Fixes 1969
* Updated affinity symbols
* Fix qemu-img rebase code to support Qemu 6.1. Ref https://github.com/GNS3/gns3-server/pull/1962
* Reinstate qemu-img rebase
* Return disk usage for partition that contains the default project directory. Fixes 1947
* Explicitly require setuptools, utils/get_resource.py imports pkg_resources