fix(RDGRS-662): server side keep alive

[OS-henriquesantos]

From chisel#442. Not tested

[OS-henriquesantos]

Tested this locally successfully.

Testing environment:

• Chisel docker container
• Outsystems Cloud Connector container
• Echo server container

docker run -d -p 7777:80 ealen/echo-server
docker run -it --rm --name chisel -p 8989:8989 -p 8888:8888 jpillora/chisel:1.9.1 server --port=8989 --reverse -v
docker run --name cloud-connector --rm -it ghcr.io/outsystems/outsystemscc:1.3.3 -v 172.17.0.1:8989 R:8888:172.17.0.1:7777

Without the fix, we could disconnect cloud connector with docker network disconnect bridge cloud-connector and then both chisel and CC would only detect the dropped connection after 15 minutes:

# docker
$ date && docker network disconnect bridge cloud-connector
Fri Aug  9 14:00:33 WEST 2024

# chisel
2024/08/09 13:16:21 server: session#1: tun: SSH disconnected
2024/08/09 13:16:21 server: session#1: tun: Unbound proxies
2024/08/09 13:16:21 server: session#1: Closed connection
2024/08/09 13:00:05.878 GET / 200 16m15s (172.17.0.1)
# cloud-connector
2024/08/09 13:14:52 client: tun: SSH disconnected
2024/08/09 13:14:52 client: Disconnected
2024/08/09 13:14:52 client: Connection error: read tcp 172.17.0.5:41100->172.17.0.1:8989: read: connection timed out
2024/08/09 13:14:52 client: Retrying in 100ms...
2024/08/09 13:14:52 client: Connection error: dial tcp 172.17.0.1:8989: connect: network is unreachable (Attempt: 1/unlimited)
2024/08/09 13:14:52 client: Retrying in 200ms...
(...)

When running a local image of chisel with this PR, chisel detects the dropped connection at most 30 seconds running with keep-alive set at 10s:

# docker 
$ date && docker network disconnect bridge cloud-connector
Fri Aug  9 17:11:07 WEST 2024

# chisel with fix
2024/08/09 16:11:17 server: session#1: tun: SSH disconnected
2024/08/09 16:11:17 server: session#1: tun: Unbound proxies
2024/08/09 16:11:17 server: session#1: Closed connection (read tcp 172.17.0.3:8989->172.17.0.1:37854: use of closed network connection)
2024/08/09 16:10:57.456 GET / 200 20s (172.17.0.1)

Since the used CC image does not have the fix, it continues stuck for 15 mins. It is expected that once the chisel dependency with this fix is updated there, that it will also detect this quickly.