esp_websocket_client: filter client received PONG response (or add event...) (IDFGH-14804)

[microfoundry]

Is your feature request related to a problem?

Currently when esp_websocket_client_recv() processes a PONG response it will be dispatched to the client event handler as a WEBSOCKET_EVENT_DATA with NULL data and zero length.

Describe the solution you'd like.

I would like to propose 3 options:

1. Filter it out all together:

/**
* esp_websocket_client_recv()
*/
        if (client->last_opcode != WS_TRANSPORT_OPCODES_PONG) {
            esp_websocket_client_dispatch_event(client, WEBSOCKET_EVENT_DATA, client->rx_buffer, rlen);
        } else {
            ESP_LOGD(TAG, "Skipping event dispatch for PONG frame.");
        }

2. Add a specific WEBSOCKET_EVENT_PONG to esp_websocket_event_id_t to allow it to be properly identified and handled by the client event function:

        if (client->last_opcode != WS_TRANSPORT_OPCODES_PONG) {
            esp_websocket_client_dispatch_event(client, WEBSOCKET_EVENT_DATA, client->rx_buffer, rlen);
        } else {
            esp_websocket_client_dispatch_event(client, WEBSOCKET_EVENT_PONG, client->rx_buffer, rlen);
        }

3. Add a define/config option for user choice.

Describe alternatives you've considered.

See above

Additional context.

I chose option 1 as I have no need to process PONG responses at an app level. But someone might find value in the distinct ability to process PONGs at an application level...