feat: use preview to compute workspace tags from terraform (#18720)

If using dynamic parameters, workspace tags are extracted using
`coder/preview`.

coderd/parameters_test.go

@@ -70,6 +70,8 @@ func TestDynamicParametersOwnerSSHPublicKey(t *testing.T) {
 	require.Equal(t, sshKey.PublicKey, preview.Parameters[0].Value.Value)
 }
 
+// TestDynamicParametersWithTerraformValues is for testing the websocket flow of
+// dynamic parameters. No workspaces are created.
 func TestDynamicParametersWithTerraformValues(t *testing.T) {
 	t.Parallel()