Improve performance of gateway by improving performance of GatewayDaemonAPI SSL

[parasj]

Fixes SKY-188

werkzeug serves the GatewayDaemonAPI over http but wasn't able to perform https at sufficient speed. This uses stunnel as an SSL reverse proxy.

$ pip install -e . && source scripts/pack_docker.sh && skylark replicate-random aws:us-east-1 aws:ap-northeast-1 --reuse-gateways -s $((1024*32))
 _____ _   ____   _______ _       ___   _   _  _____ 
/  ___| | / /\ \ / / ___ \ |     / _ \ | \ | ||  ___|
\ `--.| |/ /  \ V /| |_/ / |    / /_\ \|  \| || |__  
 `--. \    \   \ / |  __/| |    |  _  || . ` ||  __| 
/\__/ / |\  \  | | | |   | |____| | | || |\  || |___ 
\____/\_| \_/  \_/ \_|   \_____/\_| |_/\_| \_/\____/


Will transfer 4096 objects totaling 32.00GB
    VMs to provision: 1x aws:ap-northeast-1, 1x aws:us-east-1

Using overridden docker image: ghcr.io/skyplane-project/skyplane:local-5d51742800ab1321c7d3ab137508d2d2
Instances will remain up and may result in continued cloud billing. Remember to call `skyplane deprovision` to deprovision gateways.
Storing debug information for transfer in /tmp/skyplane/transfer_logs/20220615_034656/client.log
✓ Initializing cloud keys (5/5) in 4.54s
✓ Provisioning gateway instances (2/2) in 40.72s
✓ Installing gateway package (2/2) in 18.74s
🚀 32.00GB transfer job launched
  Transfer progress (4096 of 4096 chunks) ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 32.0/32.0 GiB 478.9 MB/s 0:00:00

✅ Transfer completed successfully
Transfer runtime: 70.11s, Throughput: 3.65Gbps

[linear]

SKY-188 #417 [perf] Using the https API for post_request leads to considerable slowdowns

| Replicate random performance decreases from 4Gbps per VM to 0.5Gbps per VM when using https for the post_requests endpoint: https://github.com/skyplane-project/skyplane/pull/349/files#diff-fe4dcc80574f742c411fa04f68cffedeec835da9c354bd243f57b96301e9d2c7R157-R159 |

[samkumar]

This works fine for me. I'll go ahead and merge it now.