docs: refactor documentation

[AnonymousWP]

• docs: delete CODE_OF_CONDUCT.md
• docs: delete FUNDING.yml
• docs: delete SECURITY.md
• docs: delete SPONSORS.md
• docs(contributors): move content to README
• build(ci): delete auto-comment.yml
• docs(contributing): move file to root directory
• docs(release): create RELEASE.md
• docs(contributing): refactor contributing guide
• docs(readme): add 'Next Generation' to title
• docs(contributing): explain which branching strategy we use
• chore(namings): replace reNgine by reNgine-ng`
• docs(readme): move scan engine to Wiki

[AnonymousWP]

@psyray I think most of it is done, but there are still quite some things in the Wiki and README we can / need to finetune. Perhaps we can do a call to quickly talk about it sometime this week. Feel free to review it already, but let's wait with merging before we have decided about the documentation.