SSH Gateway load test

Notice

All cases need to observe cpu and memory of the ws-proxy

Remember to delete workspaces after test, since they are always active

port-forward prometheus 9090 to local, and search graph with query like

container_memory_rss(pod="<ws-proxy-pod-name>", container="ws-proxy"}

container_cpu_rss(pod="<ws-proxy-pod-name>", container="ws-proxy"}

Prepare workspace pair AB like this:

We need to keep workspace alive, so edit gitpod-cli to build a new tmp exec file with command to keep heartbeat: send heartbeat every 30 seconds
Open a workspace A as target workspace, copy file that step1 produce to it, and exec file to keep it alive
Open a workspace B, repeat step 2

Testing in prev envs and test several cases:

Many connections to learn the cost of single connection in terms of memory and CPU

For B, write ssh connect script with connect num 10000
sh
```
go run main.go -u <workspace_url> -t <owner_token> -n <connection_num> lotconn
```
🟢 After 10000 connect exec, ws-proxy works fine, target workspace works fine, (but sender's workspace network broken)

wait: remote command exited without exit status or exit signal appear after exec command, maybe ssh gateway still has some difference with real ssh Fixed with PR
Several connection with huge amount of data back and forth

Simply exec scp with large file (dd if=/dev/zero of=test bs=1M count=1000) from A to B and B to A several times

🟢 scp 1G data works fine several times
Several connections and see how long they can stay alive with heartbeat

For B, open several terminals connect to A and exec command like htop

🟢 7 tasks of ssh command htop work and stable in 20 hours
Try dropping and reopening connections to see whether ws-proxy leaks memory on such connections
sh
```
go run main.go -u <workspace_url> -t <owner_token> -c <concurrent_num> reopen
```
🟠 Memory leak appeared and fixed by this commit

After fix