Handle `include` tag in `generate_benchmark_scripts()`

Since ogs6.4.0, PRJ files can contain an include tag that directs to an external XML file, which contains additional tags. Actually, this tag is read in Yet, there is no procedure how the respective call is created in generate_benchmark_scripts() right now. For example, the benchmark circle_1e1_axi.prj contains an include tag to refer to process tags in an external file.