implement warming in new cli tool

Adds infrastructure for calling the legacy PHP scripts. As the
CONST_* values cannot be set from the python script, hand the values
in via secret environment variables instead. These are all
temporary hacks for the transition phase to python code.

nominatim/admin/exec_utils.py

@@ -0,0 +1,21 @@
+"""
+Helper functions for executing external programs.
+"""
+from pathlib import Path
+import subprocess
+
+def run_legacy_script(script, *args, nominatim_env=None):
+        """ Run a Nominatim PHP script with the given arguments.
+        """
+        cmd = ['/usr/bin/env', 'php', '-Cq',
+               nominatim_env.phplib_dir / 'admin' / script]
+        cmd.extend(args)
+
+        env = nominatim_env.config.get_os_env()
+        env['NOMINATIM_DATADIR'] = str(nominatim_env.data_dir)
+        env['NOMINATIM_BINDIR'] = str(nominatim_env.data_dir / 'utils')
+
+        proc = subprocess.run(cmd, cwd=str(nominatim_env.project_dir), env=env)
+
+        return proc.returncode
+