Merge branch 'gpl-2'

COPYING

distro/config/apkg.toml

distro/pkg/arch/PKGBUILD

distro/pkg/deb/copyright

distro/pkg/nix/default.nix

distro/pkg/rpm/knot.spec

doc/conf.py

doc/introduction.rst

m4/ax_check_compile_flag.m4

m4/ax_check_define.m4

m4/ax_check_link_flag.m4

m4/ax_compare_version.m4

m4/ax_pkg_check_vars.m4

m4/knot-check-header.m4

m4/knot-code-coverage.m4

m4/knot-lib-version.m4

m4/knot-module.m4

m4/knot-sanitizer.m4

m4/knot-version.m4

python/knot_exporter/pyproject.toml.in