Add live timer to activities in the Azure Activity Log

[Copilot]

Issue

When performing long-running operations like deleting a resource group or a function app, the Azure Activity Log did not show a live timer indicating how long the operation has been running.

Changes Made

This PR adds a live timer to activities displayed in the Azure Activity Log:

• Modified ActivityItem.ts to add a timer display for running activities
• Added code to calculate and display the elapsed time since the activity started
• Implemented an automatic refresh mechanism that updates the timer every second
• Added proper cleanup when activities complete or error out

Before

Previously, running operations would only show the operation name without any timing information until the operation completed.

After

Now, running operations show the elapsed time since they started, updating in real-time (e.g., "Deleting resource group 'example' (1m 5s)").

Implementation Details

• Used the existing dateTimeUtils.getFormattedDurationInMinutesAndSeconds() function from vscode-azext-utils
• Added a timer that refreshes the activity display every second
• Added proper cleanup to ensure timers are disposed when no longer needed

Fixes #1144.

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