Use GCP Secrets Manager to set env vars

[zenkimoto]

Part of #39

Description of Change

Sets the following environment variables from GCP Secrets Manager:

APPROVED_DOMAINS DRIVE_ID DRIVE_TYPE EXCLUDE_FOLDERS GCP_PROJECT_ID NODE_ENV REDIRECT_URL GOOGLE_APPLICATION_JSON GOOGLE_APPLICATION_CREDENTIALS GOOGLE_APPLICATION_PUBLIC_KEY GOOGLE_CLIENT_ID GOOGLE_CLIENT_SECRET SESSION_SECRET

index.js will determine if the code is running locally and attempt to use .env file.

Related Issue

Motivation and Context

Checklist

• [ ] Ran npm run lint and updated code style accordingly
• [ ] npm run test passes
• [ ] PR has a description and all contributors/stakeholder are noted/cc'ed
• [ ] tests are updated and/or added to cover new code
• [ ] relevant documentation is changed and/or added