mgr: set argv for python in PyModuleRegistry

mgr: set argv for python in PyModuleRegistry

before this change, we setup the progname for Python interpreter,
but setup the argv for it in PyModule. and we are using deprecated
API to initialize Python interpreter.

in this change, let's do this in a single place for better
maintainability. also, take this opportunity, to use the non-deprecated
API to initialize interpreter on Python >= 3.8.

this silence the warning when compiling ceph-mgr with CPython 3.12:
```
/var/ssd/ceph/src/mgr/PyModule.cc: In member function ‘int PyModule::load(PyThreadState*)’:
/var/ssd/ceph/src/mgr/PyModule.cc:363:20: warning: ‘void PySys_SetArgv(int, wchar_t**)’ is deprecated [-Wdeprecated-declarations]
  363 |       PySys_SetArgv(1, (wchar_t**)argv);
      |       ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/python3.12/Python.h:96,
                 from /var/ssd/ceph/src/mgr/BaseMgrModule.h:4,
                 from /var/ssd/ceph/src/mgr/PyModule.cc:14:
/usr/include/python3.12/sysmodule.h:13:38: note: declared here
   13 | Py_DEPRECATED(3.11) PyAPI_FUNC(void) PySys_SetArgv(int, wchar_t **);
      |                                      ^~~~~~~~~~~~~
```

Signed-off-by: Kefu Chai <tchaikov@gmail.com>