Added a chapter on LTS to LTS upgrade

Resolves: #51313
Releases: 6.2
Change-Id: I6597323f7b60bee047c6d5a679d0e0a7c7e8fb3c
Updated the 'Troubleshooting' section

Resolves: #51313
Releases: 6.2
Change-Id: I3a5da579d6d0654660004e69ba08d94cdb7286b6
Simplified and updated Quick Install chapter

Resolves: #51313
Releases: 6.2
Updated the "In depth" section

Resolves: #51313
Resolves: #51325
Releases: 6.2