This way, any log statement for a client will include the client id,
similar to how the server now logs information about NATS clients
(such as language, version, connection name).
Also adding a debug statement once the client has successfully connected.
Here is how this will look like for a client with client id "client_0".
```
[69591] 2021/10/06 10:06:50.837977 [DBG] [::1]:57415 - mid:18 - Client connection created
[69591] 2021/10/06 10:06:50.839871 [DBG] [::1]:57415 - mid:18 - "client_0" - Client connected
[69591] 2021/10/06 10:07:00.627307 [DBG] [::1]:57415 - mid:18 - "client_0" - Client connection closed: Client Closed
```
All log statements will be affected, for instance here is an auth error:
```
[69591] 2021/10/06 10:09:48.618964 [DBG] [::1]:57424 - mid:23 - Client connection created
[69591] 2021/10/06 10:09:48.619015 [ERR] [::1]:57424 - mid:23 - "client_0" - authentication error - User "mqtt"
[69591] 2021/10/06 10:09:48.619026 [DBG] [::1]:57424 - mid:23 - "client_0" - Client connection closed: Authentication Failure
[69591] 2021/10/06 10:09:48.619038 [ERR] [::1]:57424 - mid:23 - "client_0" - unable to connect: authentication error
```
Resolves#2587
Signed-off-by: Ivan Kozlovic <ivan@synadia.com>