docs: add internal guides to repo based on catenax-ng webpage

[FaGru3n]

What would be changed or will be added with this PR?

• move and adapt format for Markdown files for our internal guides to onboarding tasks
• not in every file double checked the links and descriptions
• last remaining doc from catena-x ng website i would like to store in https://github.com/catenax-ng/cloud-infra repo
• remove specific docusaurus content and tranfer it to Markdown format like https://docusaurus.io/docs/next/markdown-features/admonitions

Why do i want to change this?

• reason Migrate catenax-ng website to eclipse tractusx eclipse-tractusx/sig-infra#348 reduce content on webpage that belongs to our current onboarding setup

Validation

• check the new files and its base content on our webpage e.g. https://catenax-ng.github.io/docs/how-to-onboard-teams-to-any-environment

[SebastianBezold]

Importing the forks to the terraform state should be removed IMO. Rest is fine