Developer manual: document registerSensitiveMethods() in logging.rst #15680

developer_manual/basics/logging.rst doesn't explain how apps keep secrets out of logged stack traces.

• Add a short section on IRegistrationContext::registerSensitiveMethods(): apps register methods that take secrets, and the logger replaces their arguments in exception stack traces.
• Add a note that this only covers stack traces: never put passwords, tokens or personal data into a log message yourself.