Reject installing/refreshing LXD snap on unsupported host OSes

[tomponline]

Please confirm

• I have searched existing issues to check if an issue already exists for the bug I encountered.

Distribution

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Distribution version

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Output of snap list --all lxd core20 core22 core24 snapd

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System info

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Instance log

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Expected behavior

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Actual behavior

The LXD docs specify supported kernels here:

https://documentation.ubuntu.com/lxd/latest/reference/releases-snap/#kernel-support

We should prevent installing & refreshing the LXD snap on hosts that do not have supported kernel versions.

Suggested my @morphis

Steps to reproduce

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Information to attach

• Any relevant kernel output (dmesg)
• Instance configuration (lxc config show <instance> --expanded)
• Main daemon log (at /var/log/lxd/lxd.log or /var/snap/lxd/common/lxd/logs/lxd.log)
• If a lxc command fails, output of the command with --debug
• Output of the daemon with --debug (or use lxc monitor while reproducing the issue)