📖 Remove roadmap.md from the book (#8544)

* 🌱 Removed Link in Roadmap.md and re-phrased the text.

* Removed roadmap.md page and Link to roadmap in summary

Author: gantanikhilraj

docs/book/src/SUMMARY.md

@@ -111,5 +111,4 @@
     - [Jobs](./reference/jobs.md)
     - [Code Review in Cluster API](./REVIEWING.md)
     - [Version Support](./reference/versions.md)
-    - [Roadmap](./roadmap.md)
     - [Supported Labels and Annotations](./reference/labels_and_annotations.md)