Include a list of Feature(Gates) and their maturity status in the docs

[fabiand]

In #251 (comment) @vladikr suggested to keep a publicly visible list of FGs.
This issue is about ensuring that this will eventually land

Is your feature request related to a problem? Please describe:
No, it's a net new enhancement

Describe the solution you'd like:
Create documentation from our code and publish it in the user-guide.

Describe alternatives you've considered:
Keep it as is.

Additional context:
See #251 (comment) for more context

[kubevirt-bot]

Issues go stale after 90d of inactivity.
Mark the issue as fresh with /remove-lifecycle stale.
Stale issues rot after an additional 30d of inactivity and eventually close.

If this issue is safe to close now please do so with /close.

/lifecycle stale

[kubevirt-bot]

Stale issues rot after 30d of inactivity.
Mark the issue as fresh with /remove-lifecycle rotten.
Rotten issues close after an additional 30d of inactivity.

If this issue is safe to close now please do so with /close.

/lifecycle rotten

[iholder101]

I think this is important and being currently worked on.
/remove-lifecycle rotten

[iholder101]

FYI @stu-gott