docs: product roadmap and zitadel versions (#9838)

# Which Problems Are Solved

The current public roadmap can be hard to understand for customers and
it doesn't show the timelines for the different versions. which results
in a lot of requests.
It only outlines what is already fixed on the timeline, but doesn't give
any possibilities to outline future topics / features, which not yet
have a timeline

# How the Problems Are Solved

A new roadmap page is added
- Outline for each version when it will have which state
- Outline different zitadel versions with its features, deprecations,
breaking changes, etc.
- Show future topics, which are not yet on the roadmap

docs/src/css/custom.css

@@ -641,3 +641,7 @@ p strong {
 .zitadel-lifecycle-deprecated {
   text-decoration: line-through;
 }
+
+table#zitadel-versions td {
+  vertical-align: top;
+}