[HAProxy] update the docs with more info on `info` dataset not being available when using HTTP for data collection

Even though it is mentioned in the docs that `info` data isn't available when using `stats` page:

[Source](https://www.elastic.co/docs/reference/integrations/haproxy)

I think it would be beneficial to add more details on it:
- protocol of data collection is configured via `hosts` configuration (for example if you configure host like `tcp://127.0.0.1:14567` it will use `tcp` protocol for data collection).
- clarify what 'using the stats page` means (it means http protocol is used for data collection).