docs(samples): Added Vertex AI Search "lite" method sample

https://cloud.google.com/generative-ai-app-builder/docs/preview-search-results#web-api-key

Author: holtskinner

discoveryengine/requirements.txt

@@ -1,2 +1 @@
-google-cloud-discoveryengine==0.12.3
-google-api-core==2.21.0
+google-cloud-discoveryengine==0.13.3

discoveryengine/search_lite_sample.py

@@ -0,0 +1,72 @@
+# Copyright 2023 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+# [START genappbuilder_search_lite]
+
+from google.api_core.client_options import ClientOptions
+from google.cloud import discoveryengine_v1 as discoveryengine
+
+# TODO(developer): Uncomment these variables before running the sample.
+# project_id = "YOUR_PROJECT_ID"
+# location = "YOUR_LOCATION"          # Values: "global", "us", "eu"
+# engine_id = "YOUR_APP_ID"
+# api_key = "YOUR_API_KEY"
+# search_query = "YOUR_SEARCH_QUERY"
+
+
+def search_lite_sample(
+    project_id: str,
+    location: str,
+    engine_id: str,
+    api_key: str,
+    search_query: str,
+) -> discoveryengine.services.search_service.pagers.SearchLitePager:
+
+    client_options = ClientOptions(
+        # For information on API Keys, refer to:
+        # https://cloud.google.com/generative-ai-app-builder/docs/migrate-from-cse#api-key-deploy
+        api_key=api_key,
+        #  For more information, refer to:
+        # https://cloud.google.com/generative-ai-app-builder/docs/locations#specify_a_multi-region_for_your_data_store
+        api_endpoint=(
+            f"{location}-discoveryengine.googleapis.com"
+            if location != "global"
+            else None
+        ),
+    )
+
+    # Create a client
+    client = discoveryengine.SearchServiceClient(client_options=client_options)
+
+    # The full resource name of the search app serving config
+    serving_config = f"projects/{project_id}/locations/{location}/collections/default_collection/engines/{engine_id}/servingConfigs/default_config"
+
+    # Refer to the `SearchRequest` reference for all supported fields:
+    # https://cloud.google.com/python/docs/reference/discoveryengine/latest/google.cloud.discoveryengine_v1.types.SearchRequest
+    request = discoveryengine.SearchRequest(
+        serving_config=serving_config,
+        query=search_query,
+    )
+
+    page_result = client.search_lite(request)
+
+    # Handle the response
+    for response in page_result:
+        print(response)
+
+    return page_result
+
+
+# [END genappbuilder_search_lite]