Outdated Parquet-java content in the developer guide

The developer guide in https://parquet.apache.org/docs/contribution-guidelines/ has mostly content related to parquet-java

Which is confusing as the parquet.apache.org site is about the format

I propose:
1. Move all parquet-java related content into the https://github.com/apache/parquet-java repo (if it isn't already there)
2. Remove all parquet-java specific content from this website (perhaps leaving links to the other implementations)

Review the developer guide at parquet.apache.org/docs/contribution-guidelines/ and compare its parquet-java-specific content with the apache/parquet-java repository. Identify content that belongs in parquet-java, remove it from the website or replace it with links to other implementations, and verify the guide is format-focused.

Written by the indexing model from the issue text.