Update reqwest

[alokedesai]

• Update reqwest to 0.12.3
• We're using an out-of-date version of reqwest, I don't think this is necessarily going to fix https://linear.app/warpdotdev/issue/CORE-1860/gh04470-implementation-of-linux-network-proxy-environment-variables but either way we should upgrade since many versions out of date.
• This PR updates the version we use to be the latest version. Note the 0.12 release put the macos proxy configuration (which Jeff added to request in Respect MacOS proxy settings seanmonstar/reqwest#1955) behind a feature flag that is enabled by default. Since we don't use the default features, I explicitly enabled the macos-system-configuration feature.