Add SBMTD Mobility Pass variables to Azure config

[thekaveman]

Following up to #1771, see a review comment that came in too late: #1771 (comment)

We don't have a way to configure the SBMTD Mobility Pass values because they aren't backed by Key Vault secrets.

E.g. we need similar terraform entries as for Courtesy Cards: https://github.com/cal-itp/benefits/blob/dev/terraform/app_service.tf#L124

Acceptance Criteria

• Each of the MOBILITY_PASS_* environment variables referenced in the data migrations is backed by a corresponding App Setting via terraform