`coder list --shared` flag

[aslilac]

Basically just needs to add shared:true to the search query, as a handy alias

[brettkolodny]

After some discussion we decided that having the flag be named --shared could be confusing to users thinking that the flag will show all shared workspaces and not just workspaces that are shared with them. So in the PR we are implementing the functionality with the flag --shared-with-me instead.