Automatically set time on WritePoint

__Proposal:__
Automatically set the time to the current time in `write.Point` if the time hasn't already been set when a call to `writeAPI.WritePoint` is made

__Current behavior:__
The time is assumed to be zero and writes to influxdb silently fail when `SetTime` isn't used

__Desired behavior:__
Automatically set the time to the current time in `write.Point` if the time hasn't already been set

__Alternatives considered:__
- `NewPoint` or `NewPointWithMeasurement` could automatically set the time to the current time

__Use case:__
Make it a little less verbose to write points and stop failing silently

Start with write.Point and the writeAPI.WritePoint entry point, then compare the alternatives involving NewPoint and NewPointWithMeasurement. The change is done when an unset point time is automatically set to the current time at the specified write boundary without overriding an explicitly set time, with coverage for both cases.

Written by the indexing model from the issue text.