Configuration publication

Let's consider a scenario where we need to publish a small configuration for multiple application instances that should promptly react to its changes.

This scenario can be implemented using semaphores in YDB coordination nodes as follows:

1. A semaphore is created (for example, named my-service-config).
2. The updated configuration is published through UpdateSemaphore.
3. Application instances call DescribeSemaphore with WatchData=true. In the result, the Data field will contain the current version of the configuration.
4. When the configuration changes, OnChanged is called. In this case, application instances make a similar DescribeSemaphore call and receive the updated configuration.