Tracker API client: add timeout to requests

[josecelano]

Parent issue: #467
Relates to: torrust/torrust-tracker#689

Since we are planning to extract a package from the Tracker for the Tracker API Client maybe we should implement this is the source package.

See torrust/torrust-tracker#689

Otherwise, we can implement it here for the time being since it's easy and later in the official "Tracker API Client". Finally, we should migrate to the official client when it's released.