fixes #2934

TODO

• split meta_/config.lua into multiple files for sections and easier maintenance and ordering of sections
• rename hijack_unnamed_buffer_when_opening as it messes up the formatting of other fields
• use (exact) classes for better UX when creating config doesn't add value as it doesn't prevent invalid fields when defining your nvim_tree.Config
• move things out of fields (hard to read) into class descriptions
• decide on lower case classnames, as nvim does for anything that's a parameter there's no real convention for other plugins, capitalised classnames match nvim-tree and general lua OO
• @type or @param everything that uses nvim_tree.Config
• ensure all links actually work - add to help check
• add gen and lint to CI
• add gen to CONTRIBUTING.md
• add an on-attach type