Add JAVA CXF openapi-feature documentation with examples from TG-search

chapters/documentation.md

@@ -67,6 +67,14 @@ For documenting RESTXQ APIs in our eXist-db systems we use the [OpenAPI4RESTXQ](
 application.
 It simply has to be installed in eXist-db and configured according to the [instructions](https://gitlab.gwdg.de/subugoe/openapi4restxq#use).
 
+##### OpenAPI for CXF Java JAXRS Applications
+
+We have not yet finished the OpenAPI documentation of our Java services, but a few tests with the [OPenAPI Feature of Apache CXF](https://cxf.apache.org/docs/openapifeature.html) have already been implemented.
+
+The outcome of this OpenAPI documentation shall be the automated generation of API doc, to be written directly IN THE CODE as Java Annotation, using the @Operation annotation, see [example](https://github.com/apache/cxf/blob/master/distribution/src/main/release/samples/jax_rs/description_openapi_v3_spring/src/main/java/demo/jaxrs/openapi/server/Sample.java#L65) and then to be read and directly be used from within a HTML page. A automatic generation of a [OpenAPI JSON file](https://dev.textgridlab.org/1.0/tgsearch-public/info/openapi.json) should be possible to use it with a [Swagger UI HTML page frontend](https://dev.textgridlab.org/1.0/tgsearch-public/info/api-docs/?url=/1.0/tgsearch-public/info/openapi.json). The question is, if we deliver that page with every service or deploy a central Swagger UI service for all the documentation. For every service endpoint such a OpenAPI doc could be provided, such as already done for [TG-search](https://dev.textgridlab.org/1.0/tgsearch-public).
+
+We also can combine this OpenAPI doc with our existing Sphinx API documentation (such as the [TG-search Sphinx API documentation](https://textgridlab.org/doc/services/submodules/tg-search/docs/index.html) as you can find [here](https://sphinxcontrib-openapi.readthedocs.io)).
+
 #### CESSDA's Software Maturity Levels in RDD (CA1.3)
 
 ##### MUST