Document gRPC's default unit in configuration properties consistently

[dlwldnjs1009]

The period and delay fields in GrpcServerHealthProperties.Schedule default to
5 seconds, but they do not declare @DurationUnit(ChronoUnit.SECONDS).

As a result, bare number values such as
spring.grpc.server.health.schedule.period=5 are bound as 5 milliseconds.

I noticed that the other Duration fields in GrpcServerProperties explicitly use
@DurationUnit(ChronoUnit.SECONDS), for example:

• Shutdown.gracePeriod
• Keepalive.time, Keepalive.timeout
• Keepalive.Permit.time
• Keepalive.Connection.maxIdleTime, maxAge, gracePeriod

I couldn't tell if the current behavior for period and delay is intentional or if
these two fields were meant to follow the same pattern.

[snicoll]

Thanks for the report.

The period and delay fields in GrpcServerHealthProperties.Schedule default to
5 seconds, but they do not declare @DurationUnit(ChronoUnit.SECONDS)

That's not really a problem. The default value of a duration-based property has no impact with the default unit. It's useful to change the default unit when seconds are obviously a better candidate than ms. For instant KeepAlive#time's default is set in hours while the default unit is seconds.

For consistency, I think it makes sense to use seconds for those two as well, and document that behavior in the description as we do elsewhere.