Add some target fields and move some things around (#3879)

In preparation for putting proxy code in the api package this creates some necessary fields in the target output and it pre-moves credential parsing and proxy handshake code to their new places. This will make the diff for the actual proxy code move quite a bit smaller.

Co-authored-by: Johan Brandhorst-Satzkorn <johan.brandhorst@gmail.com>

internal/tests/api/credentials/credentials_test.go

@@ -495,7 +495,7 @@ func TestUpdateAfterKeyRotation(t *testing.T) {
 	// Should start asynchronous rewrapping of the encrypted JSON credential
 	assert.Equal("pending", result.State)
 
-	ctx, cancel := context.WithTimeout(ctx, time.Minute)
+	ctx, cancel := context.WithTimeout(ctx, 3*time.Minute)
 	defer cancel()
 	for {
 		jobs, err := scopesClient.ListKeyVersionDestructionJobs(ctx, proj.PublicId)