docs: add k8s sec diagram

[tara-hpe]

Add k8s security diagram and update content

replaces #9572

Ticket

Description

Test Plan

Checklist

• Changes have been manually QA'd
• New features have been approved by the corresponding PM
• User-facing API changes have the "User-facing API Change" label
• Release notes have been added as a separate file under docs/release-notes/
  See Release Note for details.
• Licenses have been included for new code which was copied and/or modified from any external code

[netlify]

✅ Deploy Preview for determined-ui canceled.

Name	Link
🔨 Latest commit	525a1ce
🔍 Latest deploy log	https://app.netlify.com/sites/determined-ui/deploys/668246668bbd1d0008a9f602

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 45.93%. Comparing base (7e2e3f6) to head (525a1ce).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9593      +/-   ##
==========================================
- Coverage   51.35%   45.93%   -5.43%     
==========================================
  Files        1252     1077     -175     
  Lines      152174   139220   -12954     
  Branches     3024     3024              
==========================================
- Hits        78153    63946   -14207     
- Misses      73863    75116    +1253     
  Partials      158      158              

Flag	Coverage Δ
harness	43.27% <ø> (-29.53%)	⬇️
web	47.98% <ø> (ø)

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see 275 files with indirect coverage changes