Replace pkg_resources with importlib for Python >= 3.9

Fixes #1184

radicale/utils.py

@@ -16,12 +16,18 @@
 # You should have received a copy of the GNU General Public License
 # along with Radicale.  If not, see <http://www.gnu.org/licenses/>.
 
+import sys
 from importlib import import_module
 from typing import Callable, Sequence, Type, TypeVar, Union
 
 from radicale import config
 from radicale.log import logger
 
+if sys.version_info < (3, 8):
+    import pkg_resources
+else:
+    from importlib import metadata
+
 _T_co = TypeVar("_T_co", covariant=True)
 
 
@@ -43,3 +49,9 @@ def load_plugin(internal_types: Sequence[str], module_name: str,
                            (module_name, module, e)) from e
     logger.info("%s type is %r", module_name, module)
     return class_(configuration)
+
+
+def package_version(name):
+    if sys.version_info < (3, 8):
+        return pkg_resources.get_distribution(name).version
+    return metadata.version(name)