feat: add GET/PUT /v3/settings server settings API

GET returns all settings sections except the deprecated
VirtualBox/VMware ones (Server.Audit privilege); secrets are
masked and Controller.jwt_secret_key is excluded entirely.
PUT applies a partial update (Server.Modify privilege): masked
or empty secrets mean unchanged, null removes the option, the
response carries the new values plus restart_required, and a
settings.updated notification is emitted. New
Server.Audit/Server.Modify privileges are seeded into the
Administrator role at table creation.

gns3server/api/routes/controller/__init__.py

@@ -62,6 +62,7 @@ from . import pools
 from . import privileges
 from . import api_keys
 from . import netmiko
+from . import settings
 
 from .dependencies.authentication import get_current_active_user
 
@@ -72,6 +73,12 @@ router.include_router(
     tags=["Controller"]
 )
 
+router.include_router(
+    settings.router,
+    prefix="/settings",
+    tags=["Server settings"]
+)
+
 router.include_router(
     users.router,
     prefix="/access/users",