Fixes https://github.com/spring-projects/spring-integration/issues/3735
The `FeedEntryMessageSource` adds an url to the provided `metadataKey`
making it incompatible when we provide a `Resource`-based configuration.
* Remove adding of the url to the `metadataKey` making it rely only
on the provided value
* Remove internal `Comparator` for entries in favor of `Comparator.comparing()`
feature
* Improve some internal logic of the `PropertiesPersistingMetadataStore`
when it emits a false warning: cannot create dirs, but they are present
* Improve `feed.adoc`
bba83c7231