0.8.RC1

Added namespaces_limits service

Linux namespaces are a powerful instruments that can be used to create
sandboxes but it also exposes internal kernel interfaces to unprivileged users
which can be a source of vulnerabilities. (for example CVE-2022-25636)

New service namespaces_limits will limit amount of namespaces that
could be created inside sandbox.

It has user, mount, pid, ipc, net, time, uts and cgroup
settings which corresponds to each type of namespace. Those settings take
an integer as value with 0 (default) completely disabling creating that
type of namespace, -1 allowing unlimited amount and any positive integer
sets limit to that number. The positive integer is useful in case your application
will only create a limited number of namespaces.

Profiles might receive a well tested namespaces limits in the future version.

Dependenices changes

• GUI has been ported to PyQt6.

Build changes

• Fixed libseccomp and python-xdg being required during build.
• Added meson option to disable man page build and installation.
• Added meson install tags. Current tags are runtime for core files and cli tool,
  bubblejail-gui for gui configuration tool, fish-completion/bash-completion
  for shell autocompletion and man for man pages.
  (thank you @gordon-quad)

Known issues

• slirp4netns and namespaces_limits can conflict with each other because
  slirp4netns tries to switch to new mount namespace.
• Namespaces functions only work on x86_64 platform.