Standardize Field Naming Across Export Files

🔍Problem Statement
Export files currently use inconsistent field names for the same data across different areas of the platform. For example, the subscription ID is labeled "ID" in Subscriptions exports, the customer ID is labeled "ID" in Customers exports, and "user_ID" in other exports. This inconsistency creates unnecessary complexity for customers building integrations and automations with tools such as Zapier and other external systems.

💡User Story
As a Pelcro administrator integrating exported data with external systems, I want consistent field names across all exports so that I can build and maintain reliable automations without needing export-specific field mappings.

🎯Definition of Done

✔ Standardize field names for identical data across all export types (e.g., customer ID, subscription ID, invoice ID).

✔ Ensure existing and newly introduced exports follow the same naming convention.

✔ Update the export documentation to reflect the standardized field names.