Add returnScreenshot parameter to screenshot the final web page (#1439)

src/flaresolverr_service.py

@@ -397,6 +397,9 @@ def _evil_logic(req: V1RequestBase, driver: WebDriver, method: str) -> Challenge
 
         challenge_res.response = driver.page_source
 
+    if req.returnScreenshot:
+        challenge_res.screenshot = driver.get_screenshot_as_base64()
+
     res.result = challenge_res
     return res