Implement token fetch from URL

[s3rj1k]

Enables fetching join tokens from HTTP/HTTPS URLs in addition to local file paths. The --token-file flag now accepts URLs, allowing tokens to be served dynamically from a token server (--insecure-token-fetch flag skips TLS certificate verification when needed).

When fetching from a URL, the following query parameters are automatically appended:

• hostname - current node hostname
• arch - system architecture (e.g., amd64, arm64)
• machine-id - contents of /etc/machine-id (if available)

Implements client-side part of #6693

[s3rj1k]

Demo setup, needs at least 3 nodes to test controller and worker joining.

Need to put build artifacts into all 3 nodes manually, below is a Cheatsheet for setting up demo.

Node 1 (initial CP node):

    k0s install controller \
        --enable-dynamic-config \
        --disable-components=konnectivity-server \
        --enable-worker \
        --no-taints \
        --kubelet-root-dir=/var/lib/kubelet \
        --verbose

    systemctl enable --now k0scontroller

    k0s token create > /var/www/html/worker.token
    k0s token create --role controller > /var/www/html/controller.token

    k0s token list --role=worker
    k0s token list --role=controller

    # Needs Nginx or any other webserver
    curl http://10.42.71.101/worker.token
    curl http://10.42.71.101/controller.token

Node 2 (worker):

    k0s install worker --token-file=http://10.42.71.101/worker.token --kubelet-root-dir=/var/lib/kubelet --verbose
    systemctl enable --now k0sworker
    # journalctl -f -u k0sworker
    # k0s reset --kubelet-root-dir=/var/lib/kubelet --verbose

Node 3 (controller):

    k0s install controller \
        --enable-dynamic-config \
        --disable-components=konnectivity-server \
        --enable-worker \
        --no-taints \
        --kubelet-root-dir=/var/lib/kubelet \
        --token-file=http://10.42.71.101/controller.token \
        --verbose

    systemctl enable --now k0scontroller
    # journalctl -f -u k0scontroller
    # k0s reset --kubelet-root-dir=/var/lib/kubelet --verbose

[s3rj1k]

After disscussion with @makhov, converting this to draft for a time, we will get back to this after functionality from

• Add ability to use ENVIRON for passing bootstrap token #6727
• Add --start flag to install command #6753
• Add --token-env flag to install command #6755

would land in some way or another

[github-actions]

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