Automate new fund additions

[rishikeshsreehari]

Currently we have a cron that runs once a month to look for new funds and creates a missing_funds.json and an issue to alert the maintainer.

The maintainer then has to:

1. Review data/missing_funds.json
2. Add funds to data.json manually or run add script
3. Run fetch_nav.py to backfill historical data

While new fund additions are relatively uncommon, it is in the best interest to automate the entire process.

Ref: #46