manager: build manager and install its files with meson

• build manager and install its files with meson, manager option is disabled by default
• update packaging for manager with meson (not needed, manager build is disabled by default, old packaging is used)
• doc/build.rst (build from source):
  • update information about building knot-resolver with manager
  • add information about building knot-resolver from source with apkg (for supported distros) + instructions for installing apkg

distro/pkg/arch/PKGBUILD

@@ -45,6 +45,7 @@ build() {
         --sbindir=bin \
         -D keyfile_default=/etc/trusted-key.key \
         -D systemd_files=enabled \
+        -D manager=disabled \
         -D client=enabled \
         -D install_kresd_conf=enabled \
         -D unit_tests=enabled