style guide: added "disconnected" as preferred term

[travisamartin]

Summary

Add a new glossary entry for "disconnected" to the NGINX documentation style guide.

Background

To ensure consistency across documentation, UX, and product configuration, we're standardizing on the term "disconnected" to describe environments without internet or external network access. This aligns with the mode_of_operation: disconnected setting in NGINX Instance Manager.

Terms like "air-gapped", "offline", "network-restricted", and "dark site" have been used inconsistently. Standardizing terminology helps avoid confusion and better reflects actual usage in the product UI and configuration files.

Changes

• Added a new row to the glossary:

  | disconnected | Use this term to describe environments without internet or external network access, such as air-gapped, offline, or network-restricted setups. Preferred term due to alignment with product UI and configuration settings (e.g., `mode_of_operation: disconnected`). If needed, clarify as "in a disconnected (network-restricted) environment" for context. | |

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[mjang]

Question: are we still updating the "revision history" at the bottom of this file? (I'm OK if we want to make this an "open question" that we answer later.)

Maybe: git blame is "good enough"?