refactor: update version retrieval to use importlib.metadata

Author: Dor-bl

appium/version.py

@@ -12,4 +12,14 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-version = '6.0.0'
+from importlib import metadata
+
+
+def _get_version():
+    try:
+        return metadata.version('Appium-Python-Client')
+    except metadata.PackageNotFoundError:
+        return 'unknown'
+
+
+version = _get_version()