Add Support for Specifying Pub/Sub Subscriber Service Account ID - Pub/Sub Module

[rglenn-accenture]

Feature Request

Specify the name of the Subscriber Service Account ID via an optional variable.

Existing Naming Convention

Currently, the module bases the Subscriber Service Account ID purely on the name output of the google_pubsub_topic resource.

Recommended Solution

• New variable definition (subscriber_service_account_id) in variables.tf, with default value of "" (empty string), to set the Subscriber Service Account ID.
• New local variable in main.ts to be used in the google_service_account.pubsub_subscriber as the account_id that conditionally uses a non-empty subscriber_service_account_id value, or the existing topic-based name.
• Re-generate the modules README.md based on the new input variables.