[APIChain] enhance the robustness or url (#6008)

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I used the APIChain sometimes it failed during the intermediate step
when generating the api url and calling the `request` function. After
some digging, I found the url sometimes includes the space at the
beginning, like `%20https://...api.com` which causes the `
self.requests_wrapper.get` internal function to fail.

Including a little string preprocessing `.strip` to remove the space
seems to improve the robustness of the APIchain to make sure it can send
the request and retrieve the API result more reliably.

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Fixes # (issue)

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#### Who can review?
@vowelparrot
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langchain/chains/api/base.py

@@ -78,6 +78,7 @@ class APIChain(Chain):
             callbacks=_run_manager.get_child(),
         )
         _run_manager.on_text(api_url, color="green", end="\n", verbose=self.verbose)
+        api_url = api_url.strip()
         api_response = self.requests_wrapper.get(api_url)
         _run_manager.on_text(
             api_response, color="yellow", end="\n", verbose=self.verbose
@@ -106,6 +107,7 @@ class APIChain(Chain):
         await _run_manager.on_text(
             api_url, color="green", end="\n", verbose=self.verbose
         )
+        api_url = api_url.strip()
         api_response = await self.requests_wrapper.aget(api_url)
         await _run_manager.on_text(
             api_response, color="yellow", end="\n", verbose=self.verbose