chore(otel): Change default of trace_to_cloud to None for Agent Engine deploy

Also added --no-trace_to_cloud to allow for explicit disablement.

This is needed to distinguish between default-on telemetry and explicit disablement via old enable_tracing/trace_to_cloud flags. Same change was done to ADK templates - see https://github.com/googleapis/python-aiplatform/pull/5917/files#diff-54084046c0ff3ec289916eefbb00d04f797ebd02dc15b417fc4fc88137fd2123R439.

Co-authored-by: Kacper Jawoszek <jawoszek@google.com>
PiperOrigin-RevId: 827552868

src/google/adk/cli/cli_deploy.py

@@ -345,7 +345,7 @@ def to_agent_engine(
     temp_folder: str,
     adk_app: str,
     staging_bucket: str,
-    trace_to_cloud: bool,
+    trace_to_cloud: Optional[bool] = None,
     agent_engine_id: Optional[str] = None,
     absolutize_imports: bool = True,
     project: Optional[str] = None,

src/google/adk/cli/cli_tools_click.py

@@ -1495,11 +1495,11 @@ def cli_deploy_cloud_run(
     ),
 )
 @click.option(
-    "--trace_to_cloud",
+    "--trace_to_cloud/--no-trace_to_cloud",
     type=bool,
     is_flag=True,
     show_default=True,
-    default=False,
+    default=None,
     help="Optional. Whether to enable Cloud Trace for Agent Engine.",
 )
 @click.option(
@@ -1591,7 +1591,7 @@ def cli_deploy_agent_engine(
     region: str,
     staging_bucket: str,
     agent_engine_id: Optional[str],
-    trace_to_cloud: bool,
+    trace_to_cloud: Optional[bool],
     display_name: str,
     description: str,
     adk_app: str,