fix(source/alloydb-admin, source/cloudsql-admin): Post append new user agent (#1494)

## Description

---
Post append new user agent

## PR Checklist

---
> Thank you for opening a Pull Request! Before submitting your PR, there
are a
> few things you can do to make sure it goes smoothly:

- [x] Make sure you reviewed

[CONTRIBUTING.md](https://github.com/googleapis/genai-toolbox/blob/main/CONTRIBUTING.md)
- [x] Make sure to open an issue as a

[bug/issue](https://github.com/googleapis/genai-toolbox/issues/new/choose)
before writing your code! That way we can discuss the change, evaluate
  designs, and agree on the general idea
- [ ] Ensure the tests and linter pass
- [ ] Code coverage does not decrease (if any source code was changed)
- [ ] Appropriate docs were updated (if necessary)
- [ ] Make sure to add `!` if this involve a breaking change

🛠️ Fixes #<issue_number_goes_here>

internal/sources/alloydbadmin/alloydbadmin.go

@@ -24,8 +24,8 @@ import (
 	"go.opentelemetry.io/otel/trace"
 	"golang.org/x/oauth2"
 	"golang.org/x/oauth2/google"
-	"google.golang.org/api/option"
 	alloydbrestapi "google.golang.org/api/alloydb/v1"
+	"google.golang.org/api/option"
 )
 
 const SourceKind string = "alloydb-admin"
@@ -45,7 +45,7 @@ func (rt *userAgentRoundTripper) RoundTrip(req *http.Request) (*http.Response, e
 	if ua == "" {
 		newReq.Header.Set("User-Agent", rt.userAgent)
 	} else {
-		newReq.Header.Set("User-Agent", rt.userAgent+" "+ua)
+		newReq.Header.Set("User-Agent", ua+" "+rt.userAgent)
 	}
 	return rt.next.RoundTrip(&newReq)
 }
@@ -68,9 +68,9 @@ func newConfig(ctx context.Context, name string, decoder *yaml.Decoder) (sources
 }
 
 type Config struct {
-	Name                   string            `yaml:"name" validate:"required"`
-	Kind                   string            `yaml:"kind" validate:"required"`
-	UseClientOAuth         bool              `yaml:"useClientOAuth"`
+	Name           string `yaml:"name" validate:"required"`
+	Kind           string `yaml:"kind" validate:"required"`
+	UseClientOAuth bool   `yaml:"useClientOAuth"`
 }
 
 func (r Config) SourceConfigKind() string {

internal/sources/cloudsqladmin/cloud_sql_admin.go

@@ -45,7 +45,7 @@ func (rt *userAgentRoundTripper) RoundTrip(req *http.Request) (*http.Response, e
 	if ua == "" {
 		newReq.Header.Set("User-Agent", rt.userAgent)
 	} else {
-		newReq.Header.Set("User-Agent", rt.userAgent+" "+ua)
+		newReq.Header.Set("User-Agent", ua+" "+rt.userAgent)
 	}
 	return rt.next.RoundTrip(&newReq)
 }

tests/cloudsqlpg/cloud_sql_pg_create_instances_test.go

@@ -57,9 +57,11 @@ type masterHandler struct {
 }
 
 func (h *masterHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
-	if !strings.HasPrefix(r.Header.Get("User-Agent"), "genai-toolbox/") {
-		h.t.Errorf("unexpected User-Agent: got %q", r.Header.Get("User-Agent"))
+	ua := r.Header.Get("User-Agent")
+	if !strings.Contains(ua, "genai-toolbox/") {
+		h.t.Errorf("User-Agent header not found in %q", ua)
 	}
+
 	var body sqladmin.DatabaseInstance
 	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
 		h.t.Fatalf("failed to decode request body: %v", err)