feat: support HTTP forward proxy

[Manuthor]

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[Copilot]

Pull Request Overview

This PR adds HTTP forward proxy support to the Cosmian CLI, enabling connection through proxy servers with authentication capabilities. The implementation includes comprehensive proxy configuration options and integrates testing infrastructure to validate proxy functionality.

• Adds proxy configuration support with authentication methods (basic auth and custom headers)
• Consolidates certificate validation flags into a single --accept-invalid-certs option
• Updates submodules for KMS and Findex server components to support proxy features

Reviewed Changes

Copilot reviewed 13 out of 15 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
kms	Updates KMS submodule to include proxy support functionality
findex-server	Updates Findex server submodule for proxy compatibility
documentation/docs/cli/main_commands.md	Documents new proxy-related CLI options and consolidates cert validation flags
docker-compose.yml	Adds Squid proxy container for testing proxy functionality
crate/cli/src/tests/kms/version.rs	Adds integration test for proxy functionality using server version endpoint
crate/cli/src/tests/kms/mod.rs	Registers new version test module
crate/cli/src/tests/kms/auth_tests.rs	Adds clippy allow annotation for large stack frames
crate/cli/src/proxy_config.rs	Implements ProxyConfig struct with all proxy configuration options
crate/cli/src/lib.rs	Exports the new proxy_config module
crate/cli/src/commands.rs	Integrates proxy configuration into CLI and client setup
Cargo.toml	Removes unused cosmian_http_client dependency
.github/scripts/squid/squid.conf	Squid proxy configuration for testing with basic authentication
.github/scripts/squid/passwd	Password file for Squid proxy authentication