Add `GEMSTASH_PROTECTED_FETCH` configuration option
Add `GEMSTASH_PROTECTED_FETCH` configuration option

* https://github.com/bundler/gemstash/blob/v2.0.0/docs/gemstash-configuration.5.md#protected-fetch
* https://github.com/bundler/gemstash/blob/v2.0.0/docs/gemstash-private-gems.7.md

Intellection/docker-gemstash,Intellection/docker-gemstash