Update PostgreSQL cluster architecture diagram

[tjmoore4]

Checklist:

• [x] Have you added an explanation of what your changes do and why you'd like them to be included?
• [x] Have you updated or added documentation for the change, as applicable?
• [x] Have you tested your changes on all related environments with successful results, as applicable?
  • [ ] Have you added automated tests?

Type of Changes:

• [ ] New feature
• [ ] Bug fix
• [x] Documentation
• [ ] Testing enhancement
• [ ] Other

What is the new behavior (if this is a feature change)?

• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Replaces the existing PostgreSQL cluster architecture diagram, adds the relevant draw.io xml file, deletes the old image file and adjusts the documentation around the new image.

Also, as a separate commit, go fmt with Go 1.19 to address lint errors.

Other Information: Co-authored-by: @cbrianpace Issue: [sc-15266]