fix(coderd): ensure correct RBAC when enqueueing notifications (#15478)

- Assert rbac in fake notifications enqueuer
- Move fake notifications enqueuer to separate notificationstest package
- Update dbauthz rbac policy to allow provisionerd and autostart to create and read notification messages
- Update tests as required

testutil/notifications.go

@@ -1,49 +0,0 @@
-package testutil
-
-import (
-	"context"
-	"sync"
-
-	"github.com/google/uuid"
-)
-
-type FakeNotificationsEnqueuer struct {
-	mu   sync.Mutex
-	Sent []*Notification
-}
-
-type Notification struct {
-	UserID, TemplateID uuid.UUID
-	Labels             map[string]string
-	Data               map[string]any
-	CreatedBy          string
-	Targets            []uuid.UUID
-}
-
-func (f *FakeNotificationsEnqueuer) Enqueue(ctx context.Context, userID, templateID uuid.UUID, labels map[string]string, createdBy string, targets ...uuid.UUID) (*uuid.UUID, error) {
-	return f.EnqueueWithData(ctx, userID, templateID, labels, nil, createdBy, targets...)
-}
-
-func (f *FakeNotificationsEnqueuer) EnqueueWithData(_ context.Context, userID, templateID uuid.UUID, labels map[string]string, data map[string]any, createdBy string, targets ...uuid.UUID) (*uuid.UUID, error) {
-	f.mu.Lock()
-	defer f.mu.Unlock()
-
-	f.Sent = append(f.Sent, &Notification{
-		UserID:     userID,
-		TemplateID: templateID,
-		Labels:     labels,
-		Data:       data,
-		CreatedBy:  createdBy,
-		Targets:    targets,
-	})
-
-	id := uuid.New()
-	return &id, nil
-}
-
-func (f *FakeNotificationsEnqueuer) Clear() {
-	f.mu.Lock()
-	defer f.mu.Unlock()
-
-	f.Sent = nil
-}