[Java][Docs] Remove Java documentation from this repo

[lidavidm]

Describe the enhancement requested

IMO, we should move the Java documentation to arrow-java so it can follow the right release process. I would also like to submit for consideration the sphinx-javadoc bridge used by ADBC, which allows treating Javadoc as an Intersphinx mapping (so you don't have to hardcode links in the Sphinx source to reference Javadocs): https://github.com/apache/arrow-adbc/blob/main/docs/source/ext/doxygen_inventory.py

Component(s)

Documentation, Java

[lidavidm]

@kou should I transfer this to arrow-java too? I suppose we can keep this to remove the existing docs from this repo?