TelemetryEndpoints must be valid MutliAddr URL (#5069)

* Check for url validity when creating TelemetryEndpoints

* Update code that used TelemetryEndpoints::new()

* Update commennts that referred to TelemetryEndpoints::new()

* Add tests for telemetry

* Fix typo and fix code in docs

* Return error on failing to override telemetry

* Use expect instead of suppressing errors on must-be-valid telemetry endpoints

* Update telemetry unit tests to use expect instead of unwrap

* Implement custom deserializer for TelemetryEndpoints

* Fix typo

* Apply suggestions from code review

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>