Ensure work-item updates leave an explicit System.History marker

[BjoernOleson]

When a work-item is changed, the Azure DevOps MCP server currently appears to forward the caller-provided JSON Patch document to Azure DevOps without ensuring that the resulting revision contains an explicit history marker showing that the change was performed through the MCP server.

Azure DevOps already creates a new revision for every work-item update. However, for auditability it would be useful if MCP-driven changes were explicitly distinguishable in the work item history/discussion.

Suggested behavior:

• If the caller's patch already contains an operation for /fields/System.History, leave it unchanged.
• If the caller's patch does not contain /fields/System.History, append one automatically to the same JSON Patch request.
• Suggested default value: Updated via Azure DevOps MCP Server <version> using tool <tool>.
• Do not create a second separate update/comment; the marker should be part of the same work-item revision.
• Optionally allow the default message to be customized or disabled through server configuration.

Rationale:
This would make MCP-originated work-item changes easier to audit without requiring each individual MCP client or user prompt to remember to add history text.