samples: add Secret Manager and Parameter Manager integration samples #7582

Is your feature request related to a problem?

google.adk.integrations.secret_manager and google.adk.integrations.parameter_manager ship SecretManagerClient and ParameterManagerClient but have no sample under contributing/samples/integrations/, unlike the other GCP integrations (gcs, eventarc, bigquery, spanner, pubsub). There is also no documented pattern for using secrets from a tool without leaking the payload into the model context or session history.

Describe the solution you'd like

Two minimal samples under contributing/samples/integrations/:

• secret_manager/: an agent whose tools resolve secrets inside Python and return only non-sensitive results (a short fingerprint / status), including the regional (projects/*/locations/*/secrets/*) resource form.
• parameter_manager/: an agent whose instruction is loaded from a Parameter Manager parameter through an InstructionProvider (so operators can change behaviour by publishing a new version), plus a tool that reads a JSON runtime-configuration parameter.

Each with a README following the sample template (Overview, Sample Inputs, Graph, How To, Related Guides) and the exact gcloud commands to create the test resources.

I am working on this (Googler, change coming via the internal repo).