Undertow. Number of worker threads

[dzmitrybeinia]

Referring to documentation a number of worker threads should be 16 as minimum

https://jooby.io/#execution-model-worker-executor

but the actual number of threads by default is counted as

https://github.com/jooby-project/jooby/blob/2.x/jooby/src/main/java/io/jooby/ServerOptions.java#L72