Improve Discovery in provisioning

[Lennonka]

Goals

• Restructuring of original content
• Re-modularization
• Terminology improvements
• Beginner-friendliness
• Reduction of bloat (hopefully) and "de-spaghettization" :)
• Renamed images and image sources

For review, you can either go commit by commit or treat it as an entirely new chapter (latter recommended).

• [x] I am familiar with the contributing guidelines.

Please cherry-pick my commits into: for Foreman 3.12

• [ ] Foreman 3.11
• [ ] Foreman 3.10/Katello 4.12
• [ ] Foreman 3.9/Katello 4.11 (planned Satellite 6.15)
• [ ] Foreman 3.8/Katello 4.10
• [ ] Foreman 3.7/Katello 4.9 (Satellite 6.14)
• [ ] Foreman 3.6/Katello 4.8
• [ ] Foreman 3.5/Katello 4.7 (Satellite 6.13; orcharhino 6.6/6.7)
• [ ] Foreman 3.4/Katello 4.6 (EL8 only)
• [ ] Foreman 3.3/Katello 4.5 on EL7 & EL8 (Satellite 6.12 on EL8 only; orcharhino 6.4/6.5 on EL8 only)
• We do not accept PRs for Foreman older than 3.3.