Write a caching-policy.md file.
It should be a document about what we cache, how to configure it. Also, add a note about cache control (we use Spring Actuator on port 8085 with base path /system).

We have several caches:
1. Caches for finance instruments - assets, positions, instruments. Default configuration values - app.instruments-cache.enabled=true and app.instruments-cache.ttl=1h
2. Cache for broker accounts. Default configuration values - app.broker-accounts-cache.enabled=true and app.broker-accounts-cache.ttl=1h
user