FIX: `install.py` script fails on second run

this MR contains the following two very small meson related fixes as separate commits:

• FIX: install.py script fails on second run

  python os.symlink fails to overwrite an already existing target:
  fixed with updating the meson_version requiement to '>=0.61.0' and handling the symlink via install_symlink()

• FIX: deprecated feature used man/meson.build:

  fixes the following warning/notice:

  NOTICE: Future-deprecated features used:
  * 0.64.0: {'copy arg in configure_file'}