Add guidelines for air-gapped environments build

[torchiaf]

Summary

PR Checklists

• Do we need to backport this PR change to the Harvester Dashboard?
  • Yes, the relevant PR is at:
• Are backend engineers aware of UI changes?
  • Yes, the backend owner is:

Contributes to harvester/harvester#7258 (comment)

Test screenshot/video

Extra technical notes summary

[bk201]

@torchiaf Can we create a new section under the Rancher Integration (main menu) and provide more in-detail commands for harvester-ui-extension regarding the preparing ECI and import ECI part? It will be more user-friendly if the user doesn't have to figure out what's the image name of harvester-ui-extension.

[torchiaf]

@torchiaf Can we create a new section under the Rancher Integration (main menu) and provide more in-detail commands for harvester-ui-extension regarding the preparing ECI and import ECI part? It will be more user-friendly if the user doesn't have to figure out what's the image name of harvester-ui-extension.

The page should also contain now a section on how to install Harvester UI extension in Rancher 2.10 and higher.
harvester/harvester#7409
cc @a110605