Document that bean methods should be static when annotated with @ConfigurationPropertiesBinding

[wilkinsona]

A bean annotated with @ConfigurationPropertiesBinding should be declared static as they're created early during bean post-processing for configuration property binding. When not declared as static, the bean method's @Configuration class is created early and becomes ineligible for full post-processing.

[wilkinsona]

Re-opening to document this for @ConfigurationPropertiesBinding rather than @ConfigurationProperties.