Add support for HTTP_PROXY

[FriggaHel]

Proposed changes

This PR adds support for HTTP_PROXY (including proxies with authentication).
Also checks HTTP_PROXY right at startup to ensure sanity

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)

Checklist

• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• I have updated the json schema (if appropriate)

Further comments

[mhan83]

Validation needs another look?

🍖 HTTP_PROXY=lkadsjfadsklf ./saucectl run -c .sauce/espresso.yml
10:32:28 INF Using proxy: ://:
Running version 0.0.0+unknown
10:32:28 INF Running Espresso in Sauce Labs
10:32:28 INF Checking if ./tests/e2e/espresso/calc.apk has already been uploaded previously
10:32:28 INF Checksum: b4f9b07ac7f35639620c4a0f54605aedcb18a2ae70af1c45ea14ffaffb856618
⠋ Uploading application /Users/michaelhan/code/saucelabs/saucectl/tests/e2e/espresso/calc.apk panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x10 pc=0x1489b85]

goroutine 1 [running]:
github.com/saucelabs/saucectl/internal/http.(*AppStore).UploadStream(0x1f88500, {0xc00092170d?, 0x3e?}, {0x0?, 0x0?}, {0x1a5b960?, 0xc0000102a0?})
        /Users/michaelhan/code/saucelabs/saucectl/internal/http/appstore.go:135 +0x245
github.com/saucelabs/saucectl/internal/saucecloud.(*CloudRunner).uploadProject(0xc00009b800, {0xc00003f560, 0x1d}, {0x0, 0x0}, {0x190f53c, 0xb}, 0x0?)
        /Users/michaelhan/code/saucelabs/saucectl/internal/saucecloud/cloud.go:711 +0x60c
github.com/saucelabs/saucectl/internal/saucecloud.(*EspressoRunner).RunProject(0xc00009b800)
        /Users/michaelhan/code/saucelabs/saucectl/internal/saucecloud/espresso.go:43 +0xb3
github.com/saucelabs/saucectl/internal/cmd/run.runEspressoInCloud({{{0xc000381d90, 0x7}, {0xc000381da8, 0x8}}, {{0x0, 0x0}, 0x45d964b800}, 0x0, 0x0, {0x7ffeefbfef82, ...}, ...}, ...)
        /Users/michaelhan/code/saucelabs/saucectl/internal/cmd/run/espresso.go:183 +0x51e
github.com/saucelabs/saucectl/internal/cmd/run.runEspresso(0xc000831900, {{{{0x0, 0x0}, {0x0, 0x0}, {0x0, 0x0}, {0x0, 0x0, 0x0}}, ...}, ...}, ...)
        /Users/michaelhan/code/saucelabs/saucectl/internal/cmd/run/espresso.go:143 +0x805
github.com/saucelabs/saucectl/internal/cmd/run.Run(0x104b672?)
        /Users/michaelhan/code/saucelabs/saucectl/internal/cmd/run/run.go:236 +0x365
github.com/saucelabs/saucectl/internal/cmd/run.Command.func2(0xc000831900?, {0x190a863?, 0x2?, 0x2?})
        /Users/michaelhan/code/saucelabs/saucectl/internal/cmd/run/run.go:101 +0x2e
github.com/spf13/cobra.(*Command).execute(0xc000831900, {0xc000138020, 0x2, 0x2})
        /Users/michaelhan/go/pkg/mod/github.com/spf13/cobra@v1.2.1/command.go:860 +0x663
github.com/spf13/cobra.(*Command).ExecuteC(0xc000831400)
        /Users/michaelhan/go/pkg/mod/github.com/spf13/cobra@v1.2.1/command.go:974 +0x3b4
github.com/spf13/cobra.(*Command).Execute(...)
        /Users/michaelhan/go/pkg/mod/github.com/spf13/cobra@v1.2.1/command.go:902
main.main()
        /Users/michaelhan/code/saucelabs/saucectl/cmd/saucectl/saucectl.go:78 +0x5dc

[FriggaHel]

@mhan83: This is fixed, this was a bug in AppStorage code !