Added HAR generation as inline script

As promised yesterday, this one goes open source ;)
Really minor: I think you could actually combine this to a single `flow.server_seen` set:
```python
if flow.server_conn not in context.server_seen:
    context.server_seen.add(...)
    connect_time = ...
    if flow.server_conn.timestamp_ssl_setup:
        ssl_time = ...
```