Support and propagate HTTP options for proxy, ssl.

[mihailik]

Command line parameters for proxy, ssl root, ssl opt-in for self-signed certificates

See issue for long rationale #5423 SSL/proxy flexibility for corporate environment

This PR introduces ClientBuilderConfig in lib/wasix/src/http/client_builder.rs and corresponding CliClientBuilderConfig at lib/cli/src/config/env.rs.

These are the config options:

• proxy to specify HTTP proxy
• ca_file to specify SSL root certificate override
• unsafe_disable_ssl_verify to allow self-signed certificates

They are parsed from the command line, and passed around during runtime initialisation flow. When any HTTP request is made, ClientBuilderConfig::create_client_builder is the one producing ClientBuilder with necessary settings.

Every creation of reqwest::ClientBuilder anywhere in Wasmer codebase now goes through ClientBuilderConfig::create_builder.

Corporate environment case

SSL spoofing and seemingly insecure HTTP proxies are commonplace in large corporate environments. You just can't reach out to the big internet without a bit of customisation.

This PR allows that customisation from a command line, explicitly.

It also makes it easy to further tweaki the settings, should you need it. The options can be captured with clap:: annotations in CliClientBuilderConfig and the single central place for handling them is ClientBuilderConfig::create_client_builder.

Testing and coding style

I've updated the existing tests to account for the changes, and tried to adhere to the coding styles.

Any feedback, guidance, refactoring/naming suggestions are welcome! I'm not fussy about how this feature implemented, just really want to enable Wasmer for a possible corporate use.

[promptless]

📝 Documentation updates detected! A separate PR for documentation updates has been made here: wasmerio/docs.wasmer.io#117