feat PLM installation guide for an air-gap environment

[mikegoltsman]

feat PLM installation guide for an air-gap environment

Proposed changes

Checklist

Before sharing this pull request, I completed the following checklist:

• I read the Contributing guidelines
• My branch adheres to the Git conventions
• My content changes adhere to the F5 NGINX Documentation style guide
• If my changes involve potentially sensitive information¹, I have assessed the possible impact
• I have waited to ensure my changes pass tests, and addressed any discovered issues

Footnotes

1. Potentially sensitive information includes personally identify information (PII), authentication credentials, and live URLs. Refer to the style guide for guidance about placeholder content. ↩

[ADubhlaoich]

This functionality is not publicly called PLM and should be rephrased to match the existing document "Kubernetes (Operations improvements)".

The structure does not match the heading style of any the other installation documentation. The metadata at the top of the file is also incorrect.

It also does not use the terminology of the existing disconnected environment document ("Disconnected or air-gapped environments"), or the style that document is written in, which focuses purely on differentiating necessary steps instead of re-documenting the entire use case.