Support Multi-Select in Notification Source

[Prajwal214]

Feature Add feature issue reference Currently, users need to create separate alerts when the only variation is the Notification Source (e.g., Dashboard vs. Table). This makes the process time-consuming, especially when conditions remain the same across multiple entity types.

Describe the task A clear and concise description of what the bug is.

• Allow multi-select for Notification Source when creating alerts.
• Ensure that only common filters between selected sources are available to avoid conflicts.
• Apply this change to entities implementing EntityInterface to maintain compatibility.