feat: add support for extra headers in Tavily API requests (#55335)

* feat: add support for extra headers in Tavily API requests

* test(tavily-client): add unit tests for X-Client-Source header in API calls

* fix(tavily): add client source attribution (#55335) (thanks @lakshyaag-tavily)

---------

Co-authored-by: Nimrod Gutman <nimrod.gutman@gmail.com>

src/agents/tools/web-search-provider-common.ts

@@ -100,6 +100,7 @@ export async function postTrustedWebToolsJson<T>(
     body: Record<string, unknown>;
     errorLabel: string;
     maxErrorBytes?: number;
+    extraHeaders?: Record<string, string>;
   },
   parseResponse: (response: Response) => Promise<T>,
 ): Promise<T> {
@@ -110,6 +111,7 @@ export async function postTrustedWebToolsJson<T>(
       init: {
         method: "POST",
         headers: {
+          ...params.extraHeaders,
           Accept: "application/json",
           Authorization: `Bearer ${params.apiKey}`,
           "Content-Type": "application/json",