Remove configuration hot reloading from the target allocator

[swiatekm]

Target Allocator currently reloads configuration from the config file when it changes. This is an anti-pattern in Kubernetes - Pods should be immutable, and configuration changes should be explicitly rolled out by recreating Pods. We already restart the Target Allocator Deployment when its configuration changes since #1882. As such, the hot reload just makes the semantics more confusing without much benefit.

The plan for removing this would be:

• Add a feature flag to the target allocator to enable this, disabled by default (breaking change)
• Two versions later, remove the feature flag and the rest of the hot reload code