Outdated Parquet-java content in the developer guide

[alamb]

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)

[wgtmac]

IMHO, it might be much easier to move all these parquet-java pages under a single entry page of this developer guide instead of creating a new dedicated parquet-java website or a set of new markdown files under parquet-java.

[alamb]

IMHO, it might be much easier to move all these parquet-java pages under a single entry page of this developer guide instead of creating a new dedicated parquet-java website or a set of new markdown files under parquet-java.

That would be fine to me too -- I don't really know how the development flow in parquet-java works but I agree we should do whatever is most useful there