feat(managed-secrets): add centrally managed secrets with GITOPS_ prefix pushed to multiple targets

Introduce managed secrets owned by GitOps that can be defined once and
pushed to any combination of projects/groups across connections. Values
are stored in OS keychain, secrets appear on targets as GITOPS_{key}.

ts/opsserver/handlers/index.ts

@@ -9,3 +9,4 @@ export { WebhookHandler } from './webhook.handler.ts';
 export { ActionsHandler } from './actions.handler.ts';
 export { ActionLogHandler } from './actionlog.handler.ts';
 export { SyncHandler } from './sync.handler.ts';
+export { ManagedSecretsHandler } from './managedsecrets.handler.ts';