[Schema & Mapper] Create Spanner Tables & Mappers for Ingestion for Subscription Analytics

[jcscottiii]

Use the wrench CLI to create a new migration for the tables required by the ingestion pipeline: Analytics_SavedSearch_Feature_Map. In the same PR, implement the Go spannerMappers for these tables in lib/gcpsanner and validate them with testcontainers-go integration tests.

Spin off of #1847