Improvements to shell completions for lxc network|storage|config get|set|unset

[kadinsayani]

• lxc network|storage set|get should show configurable options;
• lxc network|storage unset should show options that can be unset;
• lxc config set|get should show configurable options based on scope;
• lxc config unset should show options that can be unset based on scope.

Completion functions should use the new scope field in the metadata configuration API to contextually source applicable options.

[kadinsayani]

From the LXD docs:

When you configure an option with global scope on any cluster member, the changes are propagated to the other cluster members through the distributed database. The locally scoped options are set only on the cluster member where you configure them, unless you use the --target flag to specify a different cluster member.

Therefore, we don't want to contextually provide completions for server configuration options based on cluster member roles.

Furthermore:

In addition to the server configuration, there are cluster member configuration options that are specific to each cluster member.

We already have completions for getting and unsetting cluster member configuration options by way of the cmpClusterMemberConfigs function, so we just need to add completions for setting cluster member configuration options.