ad-pqmon-sl: Add production testing guide

[plescaevelyn]

Add comprehensive production testing documentation for the AD-PQMON-SL power quality analyzer board. This guide is intended for manufacturing and QA teams to verify board functionality.

Content includes:

• Test duration estimates (9 min total)
• Required hardware list (Raspberry Pi 4, DAPLink, T1L cable, etc.)
• DUT assembly instructions with fasteners and board connections
• Step-by-step setup instructions with images
• DAPLink, T1L, SD card, and power connections

Test process documentation:

• Wi-Fi setup on Raspberry Pi
• 1. System Test with LCD test, LED & Button test
• Pass/fail criteria and troubleshooting for firmware upload errors
• 2. Power off procedure

Type

• Documentation
• Bug fix
• New feature
• Continuous integration

Checklist

• I have performed a self-review of changes
• I have followed the guidelines:
  • https://analogdevicesinc.github.io/documentation/contributing/docs_guidelines.html
  • https://analogdevicesinc.github.io/doctools/docs_guidelines/index.html
  • https://analogdevicesinc.github.io/documentation/contributing/creating_new_pages.html#documentation-structure
• I have used the appropriate roles and directives:
  • https://analogdevicesinc.github.io/doctools/docs_guidelines/roles.html
  • https://analogdevicesinc.github.io/doctools/docs_guidelines/directives.html
• I ensured that binary data was committed to git lfs:
  • https://analogdevicesinc.github.io/documentation/contributing/creating_new_pages.html#adding-images-and-other-binary-files
• I have built the pages I edited or created, using either make html or adoc serve:
  • https://analogdevicesinc.github.io/doctools/cli.html#serve
• I have signed-off my commits and believe my contribution improves the repository.