Create a roadmap for reactivesearch

To keeps things transparent, we should create a development and support roadmap for Reactivesearch v2 and v3.

- It should define the content of releases.
- It can include release targets, migration guides and support details.
- We can also plan out the components that are going to be added in the future releases for a current version.

Open to suggestions on this.

Related: https://github.com/nodejs/Release