dotnet: "latest" is stuck on .NET 9

[sliekens]

Hi,

While working on #1596, it came to my attention that there is a bug in the logic that resolves the latest version by comparing the STS and LTS version.

STS: 9.0.311
LTS: 10.0.103

The logic decides that in this case, STS is the latest version, because it is doing a lexicographic string comparison instead of comparing versions numerically.

So, this config is currently stuck on .NET 9:

"features": {
    "ghcr.io/devcontainers/features/dotnet:2": "latest"
}

Since this is not the first time this logic has caused problems (#1213), I want to reopen the discussion about switching to releases-index.json for determining the latest version to install. It would both simplify the version check and also make it more resilient.

I can raise the PR with the fixes.