fix: update openapi.yml to include statusChangedAt (#1187)

Fixes #1169

Update the openapi.yml to add a missing field

## Motivation and Context

openapi.yml was not in sync with live data

## How Has This Been Tested?

Validated the openapi.yml file

## Breaking Changes

No

## Types of changes
<!-- What types of changes does your code introduce? Put an `x` in all
the boxes that apply: -->
- [x] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)
- [ ] Documentation update

## Checklist
<!-- Go over all the following points, and put an `x` in all the boxes
that apply. -->
- [x] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [x] My code follows the repository's style guidelines
- [x] New and existing tests pass locally
- [ ] I have added appropriate error handling
- [ ] I have added or updated documentation as needed

## Additional context
<!-- Add any other context, implementation notes, or design decisions
-->

Signed-off-by: Jeff MAURY <jmaury@redhat.com>
Co-authored-by: Radoslav Dimitrov <radoslav@stacklok.com>

docs/reference/api/openapi.yaml

@@ -1039,6 +1039,11 @@ components:
                   description: Optional message explaining the status (e.g., deprecation reason)
                   example: "Please upgrade to version 2.0.0"
                   maxLength: 500
+                statusChangedAt:
+                  type: string
+                  format: date-time
+                  description: Timestamp when the server status was last updated
+                  example: "2023-12-01T10:30:00Z"
                 publishedAt:
                   type: string
                   format: date-time