sc: migrate signald data store to signalc

notes on data migration implementation

• use kotlin for JSON parse
• make fixture from real signald JSON (dev)
• unit test against migrating from JSON to postgres
• extend migrate func to crawl directory and migrate many JSON blobs (needs less testing)
• make this migrateDiredctory an entrypoint that is run by a gradle task
• run gradle task in dev env, see if it is possible to run signalc stack against old signalboost numbers
• feel good about shipping!