Introduce tech preview/experimental features

[mnovak]

Until now new features and API added into XTF framework had to be as stable as possible not to break backward compatibility in the future. However it's not always possible to introduce mature API. Idea is to mark such features/APIs so the consumer that it might change or be removed in the future.

One of the options might be to introduce @Experimental annotation to mark such an API.

[mchoma]

Here is interesting article regarding this topic https://dzone.com/articles/forward-looking-with-javas-deprecated. Noteworthy alternatives to introduce own annotation are are:

• Use guava's @beta annotation
• reuse javas @deprecated, e.g. @deprecated(forRemoval = false, since = 0.27)
• Handle just with comments / release notes

[simkam]

I would prefer

reuse javas @deprecated, e.g. @deprecated(forRemoval = false, since 0.27)