[devops] setup basic feature flags

[davidlhw]

Context

currently, we are nervous when pushing out new changes as it takes the risk of potentially destroying other features and functionalities.

the aim of using feature flags (ways to toggle a particular feature) is so that we can do the following with ease:

• test features in production
  • hide in progress features from users while exposing them to admins
  • A/B testing
• rollback control (break-glass scenarios)
• pave a way for more user-controlled UX related settings

Features

• MUST be able to read a config at runtime and determine which feature to toggle
• MUST be able to change this config and have prod reflect changes without any re-deployment
• SHOULD avoid storing this config on the client-side to prevent unwanted access to hidden features by the client
  • assume user has full control over client, including various data in memory like cache/stores
• SHOULD not introduce too much latency overhead

Potential Avenues to Explore

1. server-side runtime environment variables (toggle on vercel)
2. store config json file somewhere and read from it
3. integration with posthog feature flags
4. store configs on db, with a relationship to a particular user, then use nextauth to store these configs as user objects