[SE-4476] move links referencing the private docs from gitlab to private.doc.opencraft.com

Description

This MR updates most of the gitlab documentation links with equivalent links to private.doc.opencraft.com

Supporting Information

JIRA ticket: SE-4476

Gitlab Issue: #21 (closed)

Testing Instruction

1. Download the Onboarding course as a tar.gz file after changing the branch to hchandad/se-4476-fix-broken-links
2. Setup a Juniper/Koa edX devstack
3. In Studio, create a new course
4. Import the newly created zip file to the course
5. Check for all the references to the handbook are referencing to the right section or page.

Other information

• Currently not all links where updated, links which i could not find a proper equivalent where documented in this comment. Along side which changes where made to help with checking the links from the course layout.
• WIP

Reviewers