docs: Kubernetes hardening

[ppawlowski]

Description

This pull request introduces the Hardening page in the FlowFuse documentation with the Kubernetes platform hardening guides.

Related Issue(s)

Closes https://github.com/FlowFuse/engineering/issues/113

Checklist

• I have read the contribution guidelines
• Suitable unit/system level tests have been added and they pass
• Documentation has been updated
  • Upgrade instructions
  • Configuration details
  • Concepts
• Changes flowforge.yml?
  • Issue/PR raised on FlowFuse/helm to update ConfigMap Template
  • Issue/PR raised on FlowFuse/CloudProject to update values for Staging/Production
• Link to Changelog Entry PR, or note why one is not needed.

Labels

• Includes a DB migration? -> add the area:migration label

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 75.21%. Comparing base (00b8d9c) to head (3aa6a59).
⚠️ Report is 26 commits behind head on main.

Files with missing lines	Patch %	Lines
forge/setup.js	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7846      +/-   ##
==========================================
+ Coverage   75.10%   75.21%   +0.11%     
==========================================
  Files         430      432       +2     
  Lines       22844    22973     +129     
  Branches     6054     6090      +36     
==========================================
+ Hits        17157    17280     +123     
- Misses       5687     5693       +6     

Flag	Coverage Δ
backend	75.21% <0.00%> (+0.11%)	⬆️

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