Adding Tunnel.connIDs and TunnelConnectionNtf

[notthetup]

This pull request introduces enhancements to the Tunnel agent for improved connection management and observability. The main changes include the addition of connection notification messages, a new parameter to expose active connection IDs, and thread-safety improvements. These updates make it easier to monitor tunnel connections and interact with them programmatically.

Connection management and notifications:

• Added a new TunnelConnectionNtf message class to notify when a connector is opened or closed, including details such as connection status, connection ID, and connector name.
• Introduced the TunnelStatus enum to represent connection events (CONNECTED, DISCONNECTED).
• Modified the Tunnel class to send TunnelConnectionNtf notifications on connection and disconnection events, and to clean up connection tracking accordingly. [1] [2]

Parameter and API enhancements:

• Added a new read-only connIDs parameter to TunnelParam and exposed it via a getConnIDs() method in Tunnel, allowing users to query the set of active connection IDs and their associated connector names. [1] [2]
• Updated the tunnel agent's description and documentation to include the new connIDs parameter and its usage.

Thread-safety and code cleanup:

• Replaced ArrayList and HashMap with thread-safe CopyOnWriteArrayList and ConcurrentHashMap for agents, connectors, and connIDs in Tunnel, removing unnecessary synchronization blocks. [1] [2] [3] [4] [5] [6]

Testing:

• Added a new test case TunnelNotificationsTest to verify that TunnelConnectionNtf notifications are published and that the connIDs parameter is correctly reported.

[mchitre]

I don't think ReleaseNotes.md documents this as claimed in the PR description.

[notthetup]

I don't think ReleaseNotes.md documents this as claimed in the PR description.

Updated the PR.