Zuora Callback processing for SM instances depends on GitLab being alive

Problem

One of CustomersDot's responsibilities is to process Zuora Callbacks and use them to sync info regarding subscriptions (e.g., plans, CI minutes and storage packs). In the case of SM instances, this might be not ideal or necessary (see some details in this conversation (internal thread)).

Additionally, when working locally with SM-only scenarios, subscriptions sync fails if gdk is not running.

Proposal

One solution could be to guard this check with a condition (e.g. verify GitLab.com is alive, if the data processing is related to GitLab.com).