Use structured logging in logs instead of string interpolation

[Arithmomaniac]

Two related points:

• For clarity and compatability, logs should use the new log syntax, e.g. LogDebug; the old methods are just legacy compatabiltiy shims (see https://github.com/dotnet/orleans/pull/3284).
• Use placeholders instead of string interpolation. From https://blog.rsuter.com/logging-with-ilogger-recommendations-and-best-practices/:

  To ensure that a message template is correctly logged and properties are transferred as custom properties, you always need to log properties with placeholders in the correct order, e.g. logger.LogWarning("The person {PersonId} could not be found.", personId); Never use string interpolation because the replacement will be done in your application and the logging backend has no longer access to the message template and individual custom properties: logger.LogWarning($"The person {personId} could not be found."); Another downside of string interpolation is that objects are always serialized into text in your app even if the log is not actually written because there is a log level filter configured.

Together, this would turn https://github.com/OrleansContrib/Orleans.Sagas/blob/8796433b62053923bc702db0bf79fc793a3737c0/Orleans.Sagas/SagaGrain.cs#L224 into something like logger.LogDebug($"Executing activity #{activityNumber} '{currentActivityName}'...", State.NumCompletedActivities, currentActivity.GetType().Name)