Publish bazel-toolchains releases on bazel mirror

[davido]

We try to use alternative URL for fetching Bazel artifacts in WORKSPACE file, e.g.:

http_archive(
    name = "bazel_toolchains",
    sha256 = "726b5423e1c7a3866a3a6d68e7123b4a955e9fcbe912a51e0f737e6dab1d0af2",
    strip_prefix = "bazel-toolchains-3.1.0",
    urls = [
        "https://mirror.bazel.build/github.com/bazelbuild/bazel-toolchains/releases/download/3.1.0/bazel-toolchains-3.1.0.tar.gz",
        "https://github.com/bazelbuild/bazel-toolchains/releases/download/3.1.0/bazel-toolchains-3.1.0.tar.gz",
    ],
)

Is it possible to do the same for recent releases, e.g.:

https://mirror.bazel.build/github.com/bazelbuild/bazel-toolchains/releases/download/5.0.0/bazel-toolchains-5.0.0.tar.gz

Right now it's missing:

http_archive(
    name = "bazel_toolchains",
    sha256 = "1adf7a8e9901287c644dcf9ca08dd8d67a69df94bedbd57a841490a84dc1e9ed",
    strip_prefix = "bazel-toolchains-5.0.0",
    urls = [
        "https://github.com/bazelbuild/bazel-toolchains/archive/v5.0.0.tar.gz",
    ],
)

//CC @meteorcloudy

[meteorcloudy]

https://mirror.bazel.build/github.com/bazelbuild/bazel-toolchains/archive/v5.0.0.tar.gz is now available

[davido]

Thanks!