RESTEASY-2431 / create an example called resteasy-spring-undertow

[liweinan]

No description provided.

[asoldano]

@liweinan I see a testcase got removed and a main class is added and referenced in the example documentation. While this is fine for the final user, it's not ideal for us, as the example is not tested as part of the build, is it?
Would it be possible to add a testcase here?

[liweinan]

@asoldano Okay! Instead of keeping it into resteasy-spring-mvc, I have added the test case back into resteasy-spring-undertow and rewrite it.

Because the resteasy-spring-basic, resteasy-spring-mvc, resteasy-spring-customized examples shows the spring integration with servlet container running in a standalone scenario.

If we do need test cases for it, we should test the same scenario as the example shows. For resteasy-spring-basic and resteasy-spring-customized, we should use Arquillian for testing. For resteasy-spring-mvc test, it contains a frontend jsp page for testing, so we need something like testcontainer+selenium for testing. If we do need it, I can create JIRA issues to track the tasks. And for this PR we finish it by here. wdyt?

[asoldano]

@liweinan OK, fine, let's go with what we have here so far.

[liweinan]

@asoldano okay! The future work will be put into https://issues.redhat.com/browse/RESTEASY-2498