http: Close output stream in exceptional cases

- Ensure that in the case of an exception when streaming http requests,
the output stream is closed in both the success or failure cases.

- Failure to do so will result in an assertion thrown by seastar when
the output_stream goes out of scope and is deallocated.

src/v/http/client.cc

@@ -589,7 +589,7 @@ ss::future<client::response_stream_ref> client::request(
               fsend = ss::do_with(
                 request->as_output_stream(),
                 [&input](ss::output_stream<char>& output) {
-                    return ss::copy(input, output).then([&output] {
+                    return ss::copy(input, output).finally([&output] {
                         return output.close();
                     });
                 });