Update tech-specs.md to include NAP

[mkingst]

Proposed changes

There is no mention of NGINX App Protect in the tech specs for NGINX Instance Manager. NAP requires additional memory and CPU, so this needs to be mentioned,

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[mjang]

I've pushed my own "style-only" suggestions and approved.

[mkingst]

I have hereby read the F5 CLA and agree to its terms

[mjang]

Accepting / merging, since the requested change was also included in this PR.