Handle timeouts

We are facing timeouts when fetching media. Basically, FB is not responding to us even after 30 seconds, and Heroku kills the thread as it's long-running.

```ruby
client = InstagramBasicDisplay::Client.new(auth_token: user.instagram_token)
response = client.media_feed
```

Can I send a PR to add this functionality? If so, do you prefer timeout to be an environment variable or an optional param?

Start by tracing the media_feed entry point shown in the issue and reviewing how the Instagram API request is made. Decide whether the timeout should be configurable through an environment variable or an optional parameter, then verify that media fetching stops within the configured limit instead of running indefinitely.

Written by the indexing model from the issue text.