Issues Fixed

• Some Balena-related environment variables might not be present, which could result to getenv calls returning null.

Description

• Made the all response fields for the /api/v2/integrations endpoint nullable to prevent schema-related errors

Checklist

• I have performed a self-review of my own code.
• New and existing unit tests pass locally and on CI with my changes.
• I have done an end-to-end test for Raspberry Pi devices.
• I have tested my changes for x86 devices.
• I added a documentation for the changes I have made (when necessary).