Feature flag support

[linglingye001]

• Feature flags can be sourced to configMap
• Not support default and properties configMap data type when featureFlags filed set
• Refresh of feature flag is time-based, not influenced by sentinel key change
• Separator will be ignored for feature flags(consistent with CLI)

API

apiVersion: azconfig.io/v1
kind: AzureAppConfigurationProvider
metadata:
  name: appconfigurationprovider-sample
spec:
  endpoint: <app-configuration-store-endpoint>
  target:
    configMapName: configmap-created-by-appconfig-provider        
  configuration:
    selectors:
      - keyFilter: app1*
        labelFilter: common
  featureFlag:
    selectors:        
      - keyFilter: 
        labelFilter:
    refresh:   
      enabled:    
      interval: