fix: initializing KeycloakAdmin without server_url

According to the project readme, we could initialize a KeycloakAdmin object with a KeycloakOpenIDConnection object without other arguments but, server_url is required.

I made server_url optional and wrote a test for it.

src/keycloak/keycloak_admin.py

@@ -88,7 +88,7 @@ class KeycloakAdmin:
 
     def __init__(
             self,
-        server_url,
+            server_url=None,
             username=None,
             password=None,
             token=None,

tests/test_keycloak_admin.py

@@ -19,6 +19,8 @@ from keycloak.exceptions import (
     KeycloakPutError,
 )
 
+from src.keycloak import KeycloakOpenIDConnection
+
 
 def test_keycloak_version():
     """Test version."""
@@ -111,6 +113,17 @@ def test_keycloak_admin_init(env):
             is None
     )
 
+    keycloak_connection = KeycloakOpenIDConnection(
+        server_url=f"http://{env.KEYCLOAK_HOST}:{env.KEYCLOAK_PORT}",
+        username=env.KEYCLOAK_ADMIN,
+        password=env.KEYCLOAK_ADMIN_PASSWORD,
+        realm_name="master",
+        client_id="admin-cli",
+        verify=True
+    )
+    keycloak_admin = KeycloakAdmin(connection=keycloak_connection)
+    assert keycloak_admin.token
+
 
 def test_realms(admin: KeycloakAdmin):
     """Test realms.