Initially the index.look_head_time was both used to define the index.time_series.start_time and index.time_series.end_time.
The former is now controlled by index.look_back_time and the maximum value of 7 days for index.look_ahead_time is too generous. As it also delays data being indexed to new index after rollover by up to 7 days.
This PR changes the index.look_ahead_time setting's maximum allowed value from 7 days to 2 hours, which is equal to the index.look_ahead_time setting's default. A look ahead time of 2 hours is high enough to accept data that is ahead of the current time, but avoids configuring the index.look_ahead_time setting to a too high value that causes rolled over indices to not receive writes for a very long period.
This is a breaking change, but configuring the index.look_ahead_time setting to a higher value than 2 hours will not fail. Instead 2 hours will be used a look ahead time.
842303cd7f