JIRA: https://jira.spring.io/browse/INT-4153
* Remove deprecated `FeedFetcher` usage
* Introduce `Resource` based ctor for the `FeedEntryMessageSource`
* Add `SyndFeedInput` option and short-hand `preserveWireFeed` for internal `SyndFeedInput` instance
* Reflect the changes in the XSD for Feed
* Change ROME dependency from deprecated `rome-fetcher` to just `rome` as it is recommended by ROME team
* Port Java DSL for Feed module and reflect aforementioned changes in the `Feed` factory and `FeedEntryMessageSourceSpec` as well
* Document changes and mention Feed Java DSL, too
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