Deploy app in GCP test environment

[karthik-Jay]

Outcome:

• create test environment
• deploy latest version of main branch into test environment
• give developers and design team access

[c6z3h]

Attempting to break task down further...

• [x] Setup CI GitHub Actions (free for GitHub's runners on Public repositories) to check compile correctly on PR to main; in the future, run unit tests (will we even do that?!)
• [x] Setup Firebase Hosting website for Designer team access
• [x] Ensure that test site will not cost money (set up a GCP billing alert)
• [x] Ask Firebase project owner Joel Kek to downgrade BLAZE PLAN to SPARK PLAN (he's okay to keep it as is)
• [x] Setup GitHub Actions to deploy main branch to Firebase Hosting on merge https://github.com/orgs/community/discussions/26724#discussioncomment-3253093
• [x] Create a new IAM account on Firebase for purpose of deployment ${{ secrets.FIREBASE_SERVICE_ACCOUNT_MENDISPHERE }} https://github.com/FirebaseExtended/action-hosting-deploy/blob/main/docs/service-account.md
• [x] Validate build on PR works (this PR)
• [ ] Validate deploy on merge PR to main works (this PR)