Improve performance of getGenericMapResponse

[ML-Marco]

I migrate a bigger project from Springfox to Springdoc 1.8.0 (as a temporary step) and to Springdoc 2.8.3.
With Springfox the performance to generate the API definition was pretty good with approximately 5 seconds. After migrating to Springdoc 1.8.0 this increased to 20 seconds. Since the calculation happens only once this was still ok.

But with the update to Springdoc 2.8.3 it increased considerably. Now it takes 120 seconds to generate the same API definition.

I did some profiling and found this easy fix to help improve performance a little. With this fix I'm now down to 83 seconds. This is still too high and I'll try to find further improvements.

Here is a screenshot of the CPU time analysis in JProfiler. As you can see, the call to ControllerAdviceBean.findAnnotatedBeans(applicationContext) is quite expensive in total.