[Code health] Front-load anticipated breaking changes before Beta release

[gino-m]

This includes:

• [Code health] Make representation of user data (task values) more extensible #1703
  • [Code health] Support new structured submission data representation ground-android#2431
• [Code health] Use field numbers instead of names as keys in Firestore #1761
• [Code health] Rename remaining instances of field to task #936
• [Code health] Clean up remaining references to old responses field #1288
• Split survey document into multiple documents and collections #1536

Migration plan:

• Implement proto converters for Android ([Code health] Enforce structure of data in Firestore at compile-time ground-android#2049)
• Use Protocol Buffers as a Firestore schema on platform #1758
  • Implement proto converters for TypeScript
  • Define protodefs against target db structure
• [Migration: protobuf for Firestore] Introduce new schema to platform #1775
  • Implement tool in web app to write survey metadata to both old and new structure
  • Update import GeoJSON function to write to old+new structures
• [Migration: protobuf for Firestore] Introduce new schema to app ground-android#2467
  • Update Android app to write submissions to new structure
  • Update Android app to read survey metadata and LOIs in new structure
• [Migration: protobuf for Firestore] Update Cloud Functions to trigger on new metadata #1777
• [Migration: protobuf for Firestore] Update web app to read LOIs and submissions from new structure #1778
• [Migration: protobuf for Firestore] Update export functions #1779
• [Migration: protobuf for Firestore] Update Firestore and Cloud Storage rules to use new ACLs #1780
• [Migration: protobuf for Firestore] Clean up code relying on old structure #1781 and [Migration: protobuf for Firestore] Clean up code in Android using old structure ground-android#2468

@jcqli FYI

@rfontanarosa @shobhitagarwal1612 @sufyanAbbasi FYI