Implemented per OS-version artifacts

[kerberjg]

Allows to filter/specify artifacts by OS version. This is useful when a binary needs to download a different version depending on which OS version it's build for.

Eg: official LLVM is build against Ubuntu 22's GLIB (g++-12), but for Ubuntu 20 we need to get binaries from meta-flutter/llvm-toolchains instead

Will be required by #171 once meta-flutter/llvm-toolchains#1 lands

Example:

"ubuntu": [
  {
    "filename": "foo-noble.tar.xz",
    "endpoint": "/releases/.../foo-noble.tar.xz",
    "os_release": "24.04"
  },
  {
    "filename": "foo-jammy.tar.xz",
    "endpoint": "/releases/.../foo-jammy.tar.xz",
    "os_release": "22.04"
  }
]