add a configurable connection open timeout

[robbkidd]

Description:

• Resolves Hard-coded short open timeout hurts when pull-through caching on high-latency ISP #386 by making the connect open timeout configurable

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Tasks:

• Add :open_timeout to config options
  • Include Gemstash::Env::Helper in HTTPClient to make gemstash_env available as an instance method
  • Use gemstash_env to lookup new config option value when making requests
• Update docs
  • Add :open_timeout to docs and describe why someone would want to change it
  • Rephrase :fetch_timeout to make clear that it is the time for the entire open-receive-read process to complete
• Write tests
  • I do not currently know a way to test the socket open timeout in the test suite. I am open to guidance because I would love to.

✅ I will abide by the code of conduct. 💞

[robbkidd]

❯ git show
commit d2ee2ccc7ef5b48e927aaeca236deb29395f4ad8
Author: Robb Kidd <[email protected]> # lolwut?
…

❯ git config user.email
[email protected]

🤦🏻