New ThirdPartySettingsInterface and ThirdPartySettingsTrait for configuration entities to store third party settings

A new ThirdPartySettingsInterface and ThirdPartySettingsTrait are available for configuration entities to store third party settings. Previously there was no common facility for configuration to make storage of settings extensible by other modules. While Views uses plugins and stores plugin data in configuration in an extensible way, for small additional settings on configuration this is overkill. Therefore ThirdPartySettingsInterface and ThirdPartySettingsTrait were added to provide a simple extension capability.

Implement ThirdPartySettingsInterface in your configuration entity (interface) and use ThirdPartySettingsTrait in your configuration entity to support storing third party settings. Include a configuration schema snippet on the top level of your configuration for third_party_settings key. In config/schema/yourmodule.schema.yml:

     settings:
       type: .....
+    third_party_settings:
+      type: sequence
+      label: 'Third party settings'
+      sequence:
+        - type: yourconfigentity.third_party.[%key]
     otherkey:
      type: ...