Contributors docs cleanup

[limzykenneth]

Changes:

Removed merged contributor docs and archive unused ones.

@davepagurek We will merge this first and you can rebase #6866 on this after which should give a clearer picture of what's there. @Qianqianye Do review this as well to see if I missed anything.

I may do some simple formatting corrections in some of the converted docs as well because some are not rendering quite correctly in some places.

[limzykenneth]

I've created the archive folder for each language we are working on as well.

Some of the diff looks like spaces are replaced with spaces but it's actually   getting replaced with normal spaces.

[Qianqianye]

Thanks @limzykenneth! I have two questions.

Could you remind me if we included the content in contributing_documentation.md somewhere else?
Some content in the issue_labels.md that are in steward_guidelines.md, but some are not. Shall we add the missing label info somewhere or just archive it?

[limzykenneth]

For contributing_documentation.md the stuff that is not already covered are the sections for contributing examples and tutorials. One thing is that these will eventually live on the p5.js-website repo so it may make sense to have these information there instead.

For issue_labels.md I'm thinking to archive it for now first and try to rely on bots to help label things. There may need to be some clean up and adjustments to the labels eventually as we go through the 2.0 process.