docs: Fix heading hierarchy in Known Issues section

[Copilot]

Purpose

• Fixes inconsistent heading structure in DeploymentGuide.md Known Issues section that used bold text instead of proper markdown headings

Does this introduce a breaking change?

• Yes
• No

How to Test

• Get the code

git clone https://github.com/microsoft/Multi-Agent-Custom-Automation-Engine-Solution-Accelerator
cd Multi-Agent-Custom-Automation-Engine-Solution-Accelerator
git checkout copilot/sub-pr-707

• Test the code

# View the rendered markdown structure
cat docs/DeploymentGuide.md | grep -A 20 "## Known Issues"

What to Check

Verify that the following are valid

• Known Issues section uses proper markdown heading hierarchy (### → #### → #####) instead of bold text
• Heading structure matches rest of document (H2 for sections, H3 for subsections, H4/H5 for deeper levels)
• Document renders correctly in markdown viewers with proper table of contents navigation

Other Information

Before:

## Known Issues
**Unable to update/add environment variables...**
**Affected Scenarios:**
**Root Cause:**

After:

## Known Issues
### Unable to update/add environment variables...
#### Affected Scenarios:
#### Root Cause:

This enables proper document outline parsing, accessibility, and automated tooling that depends on heading structure.

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[Shreyas-Microsoft]

Closing this PR for now.
This change was created only to investigate and validate the behavior around the copilot PR being populated.
No code changes are required at this point.