Python: Support Bing Custom Search (#6278)

### Motivation and Context

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Update BingConnector to add support for Bing Custom Search, which can be
used to specify domains and webpages to search and allows custom ranking
adjustments.

### Description

<!-- Describe your changes, the overall approach, the underlying design.
These notes will help understanding how your code works. Thanks! -->
Note that API keys for Bing are separate from Bing Custom Search.

### Contribution Checklist

<!-- Before submitting this PR, please make sure: -->

- [x] The code builds clean without any errors or warnings
- [x] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [x] All unit tests pass, and I have added new tests where possible
- [x] I didn't break anyone 😄

---------

Co-authored-by: Evan Mattson <[email protected]>

python/semantic_kernel/connectors/search_engine/bing_connector.py

@@ -20,6 +20,7 @@ class BingConnector(ConnectorBase):
     def __init__(
         self,
         api_key: str | None = None,
+        custom_config: str | None = None,
         env_file_path: str | None = None,
         env_file_encoding: str | None = None,
     ) -> None:
@@ -28,12 +29,15 @@ def __init__(
         Args:
             api_key (str | None): The Bing Search API key. If provided, will override
                 the value in the env vars or .env file.
+            custom_config (str | None): The Bing Custom Search instance's unique identifier.
+                If provided, will override the value in the env vars or .env file.
             env_file_path (str | None): The optional path to the .env file. If provided,
                 the settings are read from this file path location.
             env_file_encoding (str | None): The optional encoding of the .env file.
         """
         self._settings = BingSettings.create(
             api_key=api_key,
+            custom_config=custom_config,
             env_file_path=env_file_path,
             env_file_encoding=env_file_encoding,
         )
@@ -56,8 +60,14 @@ async def search(self, query: str, num_results: int = 1, offset: int = 0) -> lis
                 params:\nquery: {query}\nnum_results: {num_results}\noffset: {offset}"
         )
 
-        _base_url = "https://api.bing.microsoft.com/v7.0/search"
-        _request_url = f"{_base_url}?q={urllib.parse.quote_plus(query)}&count={num_results}&offset={offset}"
+        _base_url = (
+            "https://api.bing.microsoft.com/v7.0/custom/search"
+            if self._custom_config
+            else "https://api.bing.microsoft.com/v7.0/search"
+        )
+        _request_url = f"{_base_url}?q={urllib.parse.quote_plus(query)}&count={num_results}&offset={offset}" + (
+            f"&customConfig={self._custom_config}" if self._custom_config else ""
+        )
 
         logger.info(f"Sending GET request to {_request_url}")
 

python/semantic_kernel/connectors/search_engine/bing_connector_settings.py

@@ -17,9 +17,11 @@ class BingSettings(KernelBaseSettings):
 
     Optional settings for prefix 'BING_' are:
     - api_key: SecretStr - The Bing API key (Env var BING_API_KEY)
+    - custom_config: str - The Bing Custom Search instance's unique identifier (Env var BING_CUSTOM_CONFIG)
 
     """
 
     env_prefix: ClassVar[str] = "BING_"
 
     api_key: SecretStr | None = None
+    custom_config: str | None = None