POC: Java Doc to improve for Java SDK V2

[ashishhk]

Review these insights and come up with a proposal on Java Docs improvement.

https://commercetools.productboard.com/insights/all-notes/notes/11234212

Convenience Features- Small helper functions. Java docs to move to official docs page. Think about Java Format Doc that w ehave currently.

AC

• [x] Move all the docs from here https://github.com/commercetools/commercetools-sdk-java-v2/blob/master/docs/ to Java Doc

• [ ] Identify all the missing topics in below list from Java SDK V2 and write down here.

[ashishhk]

@jenschude looks good as initial updates in the documentation.