Minor request: Public variables for Hourly / Daily / Minutely

[tspence]

A small request that might be easily satisfied - can the static readonly values on CronExpression.cs become public rather than private?

I noticed in my code that a common usage pattern was this:

        var scheduledTime = _configuration["AlertsScheduledJobsWorker:ScheduledTimeExpression"]
                            ?? "0 * * * *"; // By default run once per hour

I noticed this happens a half dozen times in our codebase, so I decided to replace 0 * * * * with a constant CronExpression.Hourly, and I decided to check if your library had one. It looks like those values already exist, but they are marked private. Would you accept a small PR to make these values public?

[odinserj]

Thanks, done!