Have to set firebase_site_id manually

## Expected Behavior
Comments in dev-infra.tfvars say it's optional but terraform steps fails with invalid site id

## Actual Behavior
Comments in dev-infra.tfvars say it's optional but terraform steps fails with invalid site id

## Steps to Reproduce the Problem

1. Deploy it

## Specifications

- Version:
- Platform:

Start by reading dev-infra.tfvars and the Terraform steps used for deployment. Trace how firebase_site_id is handled when it is omitted, then verify that a deployment without the variable no longer fails with an invalid site ID and that the optionality comment is accurate.

Written by the indexing model from the issue text.