refresh lxd docs based on current lxd/juju/k8s best practices

[kwmonroe]

Refresh the local install page with:

• support for lxd 5+, juju 3+, charmed k8s 1.27+
• new host sysctl section
• remove lxd apt section (hasn't been relevant since bionic/lxd 2.x)
• new lxd profile section
• calico/containerd requirements for lxd
• profile troubleshooting section

Partial fix for #830; this PR fixes the deployment, but does not include host/passthru instructions for gpu enablement.

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