The `default_enabled:` should be taken from YAML definition

Related to

#218667 (closed)

Currently we have

1. YAML with default_enabled: that provides a consistency check for all places where feature flag is used
2. Feature.enabled?(..., default_enabled: ...) that defines a desired state

This makes us to have update two places if we want to change default_enabled:. We should instead ensure that default_enabled: is always taken from YAML definition which is always loaded.

Proposal

1. Remove default_enabled: from Feature.enabled?
2. Use default_enabled: from YAML