Add mirror/keyserver override support across feature installers

[bbartels]

This PR makes feature install scripts mirror/proxy-friendly by introducing env-var-based download base URL overrides while preserving existing defaults when unset. It also adds cross-script keyserver override behavior and updates PowerShell/Ruby/dotnet flows where URL resolution/bootstrap behavior needed structural changes.

• Cross-cutting mirror/keyserver support

  • Added GITHUB_RELEASE_MIRROR support (via local GITHUB_RELEASE_URL) for GitHub Releases HTTP artifact downloads in affected scripts.
  • Updated shared get_gpg_key_servers() probing helpers to honor GPG_KEYSERVER as a single authoritative keyserver when provided.

• Per-feature URL override additions

  • github-cli: GitHub release .deb downloads now use GITHUB_RELEASE_URL.
  • nvidia-cuda: NVIDIA_REPO_URL now derives from NVIDIA_MIRROR.
  • rust: exported/persisted RUSTUP_DIST_SERVER and RUSTUP_UPDATE_ROOT.
  • go: added GO_MIRROR for tarball/signature downloads and GO_TAG_SOURCE for tag resolution.
  • node: added/exported NVM_NODEJS_ORG_MIRROR and threaded it across su ... -c boundaries.
  • java: added ADOPTIUM_API_URL (ADOPTIUM_MIRROR), and SDKMAN_SERVICE_MIRROR support via sdkman_api config rewrite.
  • php: added PHP_MIRROR, COMPOSER_MIRROR, COMPOSER_SIG_MIRROR.
  • powershell: added MICROSOFT_PACKAGES_MIRROR + GITHUB_RELEASE_URL; replaced hardcoded Microsoft/GitHub download bases.
  • kubectl-helm-minikube: added KUBECTL_MIRROR, HELM_MIRROR, MINIKUBE_MIRROR, GITHUB_RELEASE_URL; removed non-configurable kubectl fallback URL.
  • python: added PYTHON_MIRROR + GITHUB_RELEASE_URL for CPython/cosign artifacts.
  • terraform: retained CUSTOM_DOWNLOAD_SERVER; added GITHUB_RELEASE_URL for satellite tools and HASHICORP_KEY_URL (HASHICORP_GPG_KEY_MIRROR) for Noble key fetch path.
  • docker-in-docker: added GITHUB_RELEASE_MIRROR, MICROSOFT_PACKAGES_MIRROR, DOCKER_MIRROR support for compose/buildx/switch, Microsoft repo assets, and Docker CE repo/key setup.

• Required structural adjustments

  • PowerShell: removed aka.ms/powershell-release redirect-based version resolution path; version selection now relies on existing git-tag helpers.
  • Ruby:
    • Added optional git-based RVM bootstrap path when RVM_INSTALL_MIRROR is set (.../rvm/rvm.git + binscripts/rvm-installer stable ...).
    • Added /etc/rvmrc mirror entries for rvm_rubies_url and rvm_binaries_url when corresponding vars are set.
  • Dotnet:
    • DOTNET_RELEASES_INDEX_URL now uses DOTNET_RELEASES_MIRROR fallback pattern.
    • install_sdk() and install_runtime() now append --azure-feed "${DOTNET_RELEASES_MIRROR}" when set.

Example pattern applied across scripts:

GITHUB_RELEASE_URL="${GITHUB_RELEASE_MIRROR:-https://github.com}"
curl -fsSL -o artifact.deb "${GITHUB_RELEASE_URL}/owner/repo/releases/download/v${VERSION}/artifact.deb"

[bbartels]

@microsoft-github-policy-service agree

[bbartels]

Hi @abdurriq , we've been trying to get devcontainers to work internally. Unfortunately, we have an air-gapped on-prem setup here with an artifactory proxy that allows us to mirror releases/package repositories etc. This PR makes it so that an initial batch of features support overriding artifact urls so we dont need to maintain an internal fork that overrides baseurls.

[Kaniska244]

Hi @bbartels

Thank you for the contribution. However adding parameters such as the above MICROSOFT_PACKAGES_MIRROR in the installation script doesn't appear to be the complete solution for using custom mirror/ repository paths unless the respective input parameters are added in the feature configuration. Also it could be great to have additional test cases with those input parameters for respective features. Kindly let me know in case of any clarification.