[JaxRS-Spec] Fixes in generated pom

[jmini]

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• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh and ./bin/security/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\.
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Description of the PR

Several improvements in the generated POM file for the jaxrs-spec generator:

1/ Add build-helper-maven-plugin plugin in the generated pom to declare src/gen/java as sources.

=> Copied from the Jersey Jaxrs generator

The generator already output some content there:

Examples:

• src/gen/java/ in jaxrs-spec
• src/gen/java/ in jaxrs-spec-interface
• src/gen/java/ in jaxrs-spec-interface-response

2/ Jackson as dependency, because the models are using those annotations.

=> Copied from the Jersey Jaxrs generator

3/ Update javax.ws.rs-api to 2.1.1 because the @PATCH annotation (already used in the generated code) is not present in the 2.0 version.

Example Line 95:

openapi-generator/samples/server/petstore/jaxrs-spec/src/gen/java/org/openapitools/api/FakeApi.java

Lines 95 to 101 in 526e980

	@PATCH
	@Consumes({ "application/json" })
	@Produces({ "application/json" })
	@ApiOperation(value = "To test \"client\" model", notes = "To test \"client\" model", response = Client.class, tags={ "fake", })
	@ApiResponses(value = {
	@ApiResponse(code = 200, message = "successful operation", response = Client.class)
	})

[wing328]

LGTM