Bug Report: (codecov/codecov-api) Regression in 24.11.1: GitLab OAuth signup fails due to unchecked Pub/Sub initialization

[CerebralXor]

In version 24.11.1, a regression was introduced in PR codecov/codecov-api#940 (commit codecov/codecov-api@8d317ae) where the new ShelterPubsub implementation unconditionally tries to initialize a Google Cloud Pub/Sub client, even when Pub/Sub is not configured. This causes user signup to fail when using GitLab OAuth.

The previous implementation (commit codecov/codecov-api@63bcae7) had a guard clause that only initialized Pub/Sub if both project_id and topic_id were configured. This guard was lost in the refactor.

Steps to reproduce:

Deploy self-hosted with the codecov/self-hosted-api:24.11.1 container image and without any Google Cloud Pub/Sub configuration
Attempt to sign up using GitLab OAuth
Signup fails with error:
google.auth.exceptions.DefaultCredentialsError: Your default credentials were not found
Fix suggestion:
Add a guard clause in ShelterPubsub.init to only initialize the Pub/Sub client if both SHELTER_PUBSUB_PROJECT_ID and SHELTER_PUBSUB_SYNC_REPO_TOPIC_ID are configured.