* GH-3938: Fix HTTP XML configuration for ambiguity
Fixes https://github.com/spring-projects/spring-integration/issues/3938
The `encoding-mode` is a property of the `RestTemplate`.
Therefore, it cannot be set on the component configuration together with
an externally injected `rest-template`
Even if `HttpRequestExecutingMessageHandler` has an assertion for such
an ambiguity, the XML parser just ignores this `encoding-mode`
when it encounters the `rest-template`
* Fix `HttpAdapterParsingUtils.verifyNoRestTemplateAttributes()` to check for not allowed
attributes with a `encoding-mode` as well
* Remove a `default` from the `encoding-mode` to not cause an ambiguity in the parser
* Fix some typos in the `spring-integration-http.xsd`
* Rework `OutboundResponseTypeTests` to JUnit 5
**Cherry-pick to `5.5.x`**
* * Fix error handling for `encoding-mode` in the `HttpAdapterParsingUtils`
* Cover `encoding-mode` and `rest-template` ambiguity with a test against failing XML configuration
* * Improve error message for ambiguous attributes in the `HttpAdapterParsingUtils`
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