feat(cli): add enterprise external-workspaces CLI command (#19287)

This pull request introduces support for external workspace management, allowing users to register and manage workspaces that are provisioned and managed outside of the Coder.

* coder external-workspaces create - Creates a new external workspace (this command extends coder create)
  * Example: coder external-workspaces create ext-workspace --template=externally-managed-workspace -y
  * Checks if template has coder_external_agent resource before creating a workspace
* coder external-workspaces list - Lists all external workspaces
* coder external-workspaces agent-instructions <workspace name> <agent name> - Retrieves agent connection instruction
  * Example: coder external-workspaces agent-instructions ext-workspace main --output=json

cli/root.go

@@ -108,7 +108,7 @@ func (r *RootCmd) CoreSubcommands() []*serpent.Command {
 		// Workspace Commands
 		r.autoupdate(),
 		r.configSSH(),
-		r.create(),
+		r.Create(CreateOptions{}),
 		r.deleteWorkspace(),
 		r.favorite(),
 		r.list(),