Enable `CONFIG_MEMTEST` for running a quick RAM test during boot with the kernel arg `memtest`

[ChrisIgel]

It would be nice to have the option to use the memtest kernel arg during boot to execute a quick RAM test.

Also: Is there / will there be an option to automatically trigger a periodic restart of some/all of the nodes in the cluster without an external system running talosctl commands for instance?

[github-actions]

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