[Bug]: image fetch honors `HTTP_PROXY` but not other standard variables.

[jglogan]

I have done the following

• I have searched the existing issues
• If possible, I've reproduced the issue using the 'main' branch of this project

Steps to reproduce

All of HTTP_PROXY, HTTPS_PROXY, and NO_PROXY, both upper and lower case, should be checked. This should be in a utility function so that clients in container can use common code.

See:

• related issue [Bug]: Kernel download honors HTTP_PROXY but not other standard environment variables. container#466 with expected and actual results
• a pretty decent reference article
• relevant code

Current behavior

see apple/container#466

Expected behavior

see apple/container#466

Environment

- OS: 15.6
- Swift: 16.4
- Xcode: container CLI version 0.3.0 (build: release, commit: 3fcf647)

Relevant log output

Code of Conduct

• I agree to follow this project's Code of Conduct

[SuzukiHonoka]

Thanks, I tested the 'HTTP_PROXY', but it does not work too, I don't see the traffic for downloding kernel at all.
Environment check:

# printenv|grep PROXY
HTTP_PROXY=http://127.0.0.1:10828
HTTPS_PROXY=http://127.0.0.1:10828

[jglogan]

An approach that allows Containerization clients to specify proxy policy and other config would be to:

• Have a proxy utility that implements the correct proxy policy above (include unit tests).
• Change RegistryClient to accept an HttpClient.Configuration, instead of hardcoding (an incomplete) proxy policy above. The convenience init() call could just specify a basic configuration. See https://github.com/apple/containerization/blob/main/Sources/ContainerizationOCI/Client/RegistryClient.swift#L111-L122.
• Update ImageStore pull/push to also accept the configuration argument.