Migrate Slapos to 3.9

The goal is to be able to build slapos-node with python3.9.

Python 3.9 needs a newer version of gobject-introspection, which the new gobject-introspection requires to switch the build system from configure to the meson. Same as the pygobject.

gobject-introspection: Version upgrade: 1.50.0 → 1.76.1 pygobject: Version upgrade: 3.22.0 → 3.44.2

Added Meson-specific setup commands in pre-configure and configure-command. Updated environment variables for Meson compatibility. Removed obsolete autotools configuration options.

Verified that gobject-introspection and pygobject are correctly built using the Meson build system and linked to required dependencies (glib, ninja, pcre2, etc.).