SPIKE: Set up fastlane for automated app signing and builds

**Describe the task**
Set up fastlane infra so we don't have to manually sign/distribute mobile apps (e.g. FBP Go)

**Acceptance Criteria**
- [ ] Fastlane is running as part of CI/CD in FBP Go pipeline
- [ ] Developer can run a command to automatically sign app with new and existing certs
- [ ] Developer can run a command automatically upload app to testflight/play store

**Additional context**
- https://fastlane.tools
- See RC thread for convo: https://chat.developer.gov.bc.ca/channel/devops-mobile-development?msg=Zn56WyuHYp2bkKwRc

Start by reviewing the FBP Go pipeline and the linked RC thread to understand the existing mobile build and signing flow. Done means fastlane runs in CI/CD, developers have commands for signing with new and existing certificates, and builds can be uploaded to TestFlight or the Play Store.

Written by the indexing model from the issue text.