[GR-60094] Revisit top-level README.md to explain the new repository structure.

[olyagpl]

No description provided.

[olyagpl]

Having just consulted with @sachin-pikle, and we think it's still good to have a full list of examples on the home page, similar to Spring Boot experience https://github.com/spring-projects/spring-data-examples. Then a visitor can search by a word and find what he looks for. I'll push another commit, hold on with reviewing this PR.

[olyagpl]

I have finished rewriting this repository README and listed each actively tested demo in it. Each demo is linked to its source code and has a short description of its purpose.
A reminder of the structure levels:

• native-image
  • build
  • benchmarks
  • clouds
  • configure
  • containerize
  • debug (there is no Java example app that we can source here yet)
  • microservices (currently only micronaut demos, I'll add Spring demo later)
  • monitor
  • optimize
• compiler (currently only one demo)
• archive (polyglot demos and from blogs)

Second, this PR also remove GraalJS, GraalPy, and GraalWasm directories and I added a paragraph in README, at the beginning, where to find Graal Languages Demos.

Lastly, this PR moves /graalvm-demos/clouds/ under /graalvm-demos/native-image/demos, that's why there are so many changed files in this PR (they were only moved).