Return dependency metadata from module extension

[mortenmj]

This allows use_repo() calls in MODULE.bazel to be automagically created. With a MODULE.bazel containing e.g.

apk = use_extension("@rules_apko//apko:extensions.bzl", "apko")
apk.toolchain(
    apko_version = "v0.14.2"
)
apk.translate_lock(
    name = "my_image",
    lock = "//my_image:apko.lock.json",
)

running bazel mod tidy would generate (or update) a use_repo() expression like so:

use_repo(apk, "apko_toolchains", "my_image")